Add ArrowFunctionExpression to opaqueTypes

[yavorsky]

Using arrow functions inside generators:

function* gen () {
  const a = () => { 
    return 1 
  };
};

throws:

Error: src/index.js: unknown Expression of type "ArrowFunctionExpression"
    at /Users/aqson/Development/temp/babel-preset-env-issue-160/node_modules/regenerator-transform/lib/emit.js:1035:15

But works fine with FunctionExpressions and arrow functions without BlockStatements:

function gen* {
  const a = () => 1;
};

function gen2* {
  const a = function () {
    return 1;
  };
};

The root of the problems lies in the explodeStatement method where we check node for the leaps and 2 of working cases returns false, but the one with ArrowFunctionExpression + BlockStatement - true.

Resolves: babel/babel-preset-env#160 and other cases without babel-plugin-transform-es2015-arrow-functions.

[facebook-github-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla - and if you have received this in error or have any questions, please drop us a line at cla@fb.com. Thanks!

If you are contributing on behalf of someone else (eg your employer): the individual CLA is not sufficient - use https://developers.facebook.com/opensource/cla?type=company instead. Contact cla@fb.com if you have any questions.

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[benjamn]

This makes a ton of sense!