fix: compile dependencies with babel

see: sindresorhus/ama#446

rollup.config.js

@@ -2,6 +2,9 @@ import resolve from 'rollup-plugin-node-resolve'
 import commonjs from 'rollup-plugin-commonjs'
 import babel from 'rollup-plugin-babel'
 import pkg from './package.json'
+import fs from 'fs'
+
+const babelrc = JSON.parse(fs.readFileSync('./.babelrc', 'utf8'))
 
 export default [
   {
@@ -14,7 +17,13 @@ export default [
     plugins: [
       resolve(),
       commonjs(),
-      babel(),
+      babel({
+        // compile some libraries of sindresorhus with babel, because these are using es2015+ syntax but with commonjs.
+        // see: https://github.com/rollup/rollup-plugin-babel#external-dependencies
+        ...babelrc,
+        babelrc: false,
+        include: '**',
+      }),
     ],
   },
 ]