Dependency Update February-April 2019

This is the regular batch update for outdated production and development
dependencies.

The largest change is the migration to MDX 1.0.0 (1) using the official
migration guide for v0 to v1 (2).

React has been been updated to the latest patch version 16.8.6 (3) and
the `prop-types` package now comes with a handy new `elementType`
prop type (4) that can be used for React components.

`polished` has been updated to the large 3.0.0 version milestone (5)
that comes with many features in form of new modules, improvements like
a new error system as well as a a roadmap for v4.
The `readableColor` helper now offers the option to set the color(s) it
returns for light or dark colors instead of only returning `white` or
`black` based on the passed colors luminosity. `stripUnit` now offers
the option to return the value and unit as an array, replacing the
functionality of `getValueAndUnit` that'll is now deprecated and will be
removed in v4.
All color modules will now also safely handle the `transparent` keyword
instead of erroring out.
See the release notes for all details and changes.

React Waypoint has been updated to major version 9 (6) that comes with
improvements in library size and minifications in form of named exports
for the `Waypoint` module as well as for all defined constants.

Prettier 1.17.0 (7) now allows to use shared configurations making it
much easier to setup new projects and keep the config code base at one
single-point-of-truth. Also Markdown tables are now kept compact when
reformatting would exceed the print width (8) making largely improving
the readability.

Gatsby and all official plugins have been updated to the latest
versions. This comes with new features that allow environment variables
to be replaced per environment (9).

`gatsby-plugin-manifest` fixes the incorrect favicons size bug (10) that
often appeared as warning in the console.

`gatsby-plugin-sharp` now comes with a `defaultQuality` option (11) to
define the default quality for processed images instead of only allowing
to set the quality through the GraphQL query.

`gatsby-image` now comes with a `durationFadeIn` option (12) that
accepts a number instead of boolean to customize animation duration.

>>>>>> Production Dependencies

- @babel/polyfill `7.2.5` -> `7.4.3`
- @mdx-js/tag `0.18.0` -> `0.20.3`
- gatsby `2.0.75` -> `2.0.117`
- gatsby `2.1.4` -> `2.3.29`
- gatsby-image `2.0.30` -> `2.0.40`
- gatsby-mdx `0.4.0` -> `0.6.2`
- gatsby-plugin-canonical-urls `2.0.10` -> `2.0.12`
- gatsby-plugin-catch-links `2.0.10` -> `2.0.13`
- gatsby-plugin-google-gtag `1.0.13` -> `1.0.16`
- gatsby-plugin-lodash `3.0.4` -> `3.0.5`
- gatsby-plugin-manifest `2.0.17` -> `2.0.29`
- gatsby-plugin-netlify `2.0.9` -> `2.0.15`
- gatsby-plugin-offline `2.0.23` -> `2.0.25`
- gatsby-plugin-react-helmet `3.0.6` -> `3.0.12`
- gatsby-plugin-remove-trailing-slashes `2.0.7` -> `2.0.11`
- gatsby-plugin-sharp `2.0.23` -> `2.0.35`
- gatsby-plugin-sitemap `2.0.5` -> `2.0.12`
- gatsby-plugin-styled-components `3.0.5` -> `3.0.7`
- gatsby-plugin-svgr `2.0.1` -> `2.0.2`
- gatsby-source-filesystem `2.0.20` -> `2.0.32`
- gatsby-source-graphql `2.0.10` -> `2.0.18`
- gatsby-transformer-sharp `2.1.15` -> `2.1.18`
- gatsby-transformer-yaml `2.1.8` -> `2.1.12`
- inter-ui `3.3.2` -> `3.5.0`
- polished `2.3.3` -> `3.2.0`
- prop-types `15.6.2` -> `15.7.2`
- react `16.8.3` -> `16.8.6`
- react-dom `16.8.3` -> `16.8.6`
- react-pose `4.0.6` -> `4.0.8`
- react-spring `8.0.7` -> `8.0.19`
- react-waypoint `8.1.0` -> `9.0.2`
- semver `5.6.0` -> `6.0.0`
- styled-components `4.1.3` -> `4.2.0`
- typeface-rubik `0.0.54` -> `0.0.72`

>>>>>> Development Dependencies

- @babel/core `7.2.2` -> `7.4.3`
- @babel/plugin-proposal-class-properties `7.3.0` -> `7.4.0`
- @babel/plugin-proposal-nullish-coalescing-operator `7.2.0` -> `7.4.3`
- @mdx-js/mdx `0.20.1` -> `1.0.14`
- @mdx-js/tag `0.18.2` -> `0.20.3`
- @svgr/webpack `4.1.0` -> `4.2.0`
- babel-jest `24.1.0` -> `24.7.1`
- babel-plugin-react-remove-properties `0.2.5` -> `0.3.0`
- babel-preset-gatsby `0.1.7` -> `0.1.11`
- eslint `5.14.0` -> `5.16.0`
- eslint-plugin-import `2.16.0` -> `2.17.2`
- eslint-plugin-react-hooks `1.0.2` -> `1.6.0`
- husky `1.3.1` -> `2.1.0`
- jest `24.1.0` -> `24.7.1`
- jest-dom `3.0.2` -> `3.1.3`
- jest-junit `6.2.1` -> `6.3.0`
- lint-staged `8.1.3` -> `8.1.5`
- prettier `1.16.4` -> `1.17.0`
- react-testing-library `5.5.3` -> `6.1.2`
- webpack-bundle-analyzer `3.0.3` -> `3.3.2`

References:
  (1) https://mdxjs.com/blog/v1
  (2) https://mdxjs.com/migrating/v1
  (3) https://github.com/facebook/react/releases/tag/v16.8.6
  (4) facebook/prop-types#211
  (5) https://github.com/styled-components/polished/releases/tag/v3.0.0
  (6) https://github.com/brigade/react-waypoint/releases/tag/v9.0.0
  (7) https://prettier.io/blog/2019/04/12/1.17.0.html
  (8) https://prettier.io/blog/2019/04/12/1.17.0.html#do-not-align-table-contents-if-it-exceeds-the-print-width-and-prose-wrap-never-is-set-5701-by-chenshuai2144
  (9) gatsbyjs/gatsby#10565
  (10) gatsbyjs/gatsby#12081
  (11) gatsbyjs/gatsby@8af9826
  (12) gatsbyjs/gatsby#13566

GH-137