chore: bump dependencies

[KubaJastrz]

Changes:

• upgraded all dependencies and devDependencies
• updated configuration for jest, eslint, prettier, husky and lint-staged
• linted all files
• wrapped paths with slash to fix tests failing on Windows after stylelint@13 breaking changes
• removed babel plugins from @babel/parser config that are already supported (in latest 7.8.3 version)

This has been done in preparations for #231

[coveralls]

Coverage remained the same at 100.0% when pulling 40cd776 on KubaJastrz:maintenance into d61ab3d on styled-components:master.

[chinesedfan]

@KubaJastrz Really appreciate your work. I almost want to merge it directly except for a few questions.

wrapped paths with slash to fix tests failing on Windows after stylelint@13 breaking changes

Can you elaborate what breaking changes are?

removed babel plugins from @babel/parser config that are already supported (in latest 7.8.3 version)

Do you mean those plugins have been added by default? And what's your reason about adding funciton-sent?

This has been done in preparations for #231

Would you mind explaining your plan a little more? Just want to confirm in advance and to avoid changes in vain.

[KubaJastrz]

Can you elaborate what breaking changes are?

It seems like stylelint/stylelint#4254 prevents us from passing fixture file paths directly into stylelint.lint({ files: [fixture] }) config on Windows, because it uses backward slashes, hence this change:

- fixture = path.join(__dirname, './fixtures/...')
+ fixture = slash(path.join(__dirname, './fixtures/...'))

Instead of slash library we could use path.posix.join, but then all tests like this would fail because stylelint returns back original paths:

it('should use the right file', () => {
  expect(data.results[0].source).toEqual(fixture)
})

---

Do you mean those plugins have been added by default? And what's your reason about adding function-sent?

Yes, for example @babel/parser supports nullishCoalescingOperator, optionalChaining and dynamicImport since 7.8.0, objectRestSpread were asyncGenerators already supported in ES2018: babel/babel#8448

I didn't add function-sent, it just appears green because of the removed comma ,.

---

Would you mind explaining your plan a little more? Just want to confirm in advance and to avoid changes in vain.

I would like to look at #231, but I wanted to make sure that we are using latest @babel/core first, which added support for new configuration files that could come in handy.

[chinesedfan]

Thanks for @KubaJastrz's detailed explanations. You can go ahead for #231. Before merging, I will wait for days to listen advices from @emilgoldsmith and @mxstbr.