Explicitly specify ts and tsx extensions in babel options (#96)

* fix: explicitly specify ts and tsx extensions in babel options

rollup-plugin-typescript2 transpiles the code but doesn't change the
file extensions. Files with ts and tsx extentions aren't processed by
Babel by default so we need to add those extensions to the babel config.

* Patch/extend @babel/core types

src/createRollupConfig.ts

@@ -1,3 +1,4 @@
+import { DEFAULT_EXTENSIONS } from '@babel/core';
 import { safeVariableName, safePackageName, external } from './utils';
 import { paths } from './constants';
 import { terser } from 'rollup-plugin-terser';
@@ -14,6 +15,7 @@ const replacements = [{ original: 'lodash', replacement: 'lodash-es' }];
 
 const babelOptions = {
   exclude: /node_modules/,
+  extensions: [...DEFAULT_EXTENSIONS, 'ts', 'tsx'],
   plugins: [
     'annotate-pure-calls',
     'dev-expression',

src/env.d.ts

@@ -5,6 +5,13 @@ declare module 'ora';
 declare module 'sade';
 declare module 'tiny-glob/sync';
 declare module 'ansi-escapes';
+
+// Patch Babel
+// @see line 226 of https://unpkg.com/@babel/core@7.4.4/lib/index.js
+declare module '@babel/core' {
+  export const DEFAULT_EXTENSIONS: string[];
+}
+
 // Rollup plugins
 declare module '@jaredpalmer/rollup-plugin-preserve-shebang';
 declare module 'rollup-plugin-babel';