Use default export instead of export = styles

[ddanielbee]

Situation

I'm currently using typed-css-modules to generate css-modules types in a snowpack project that uses @babel/plugin-transform-typescript under the hood.

Problem

When building, I get the following error:

`export =` is not supported by @babel/plugin-transform-typescript
  Please consider using `export <value>;`.

Solution

To solve this issue, we can change this line:

typed-css-modules/src/dts-content.ts

Line 53 in 3b9f9e5

'export = styles;',

To 'export default styles;',

I'll work on a PR for it, but in the meantime, do you see any issues with this approach?