BREAKING: Handle ES2018 capture names (#247)

Use RegExpIdentifierName for named captures/backreferences to match ES2018, and update build tools to make it work

Author: josephfrazier

.babelrc

@@ -1,5 +1,6 @@
 {
   "plugins": [
+    ["@babel/plugin-proposal-unicode-property-regex", { "useUnicodeFlag": false }],
     [
       "@babel/plugin-transform-runtime",
       {

.eslintrc.js

@@ -7,6 +7,7 @@ module.exports = {
     },
     "extends": "eslint:recommended",
     "parserOptions": {
+        "ecmaVersion": 9,
         "sourceType": "module"
     },
     "rules": {