fix(build): include relevant polyfill and babel transforms to be comp…

…atible with IE 11

example.js

@@ -1,3 +1,6 @@
+// import this polyfill in order to make webapp compatible with IE 11
+import 'es6-math'
+
 import { createHashHistory } from 'history'
 import { connectRouter, routerMiddleware } from 'connected-react-router'
 import React, { Component } from 'react'

package.json

@@ -34,7 +34,6 @@
     "clone": "^2.1.0",
     "connected-react-router": "^5.0.1",
     "copy-to-clipboard": "^3.0.8",
-    "core-js": "2",
     "currency-formatter": "^1.4.2",
     "d3-selection": "^1.3.0",
     "d3-zoom": "^1.7.1",
@@ -78,7 +77,8 @@
   },
   "devDependencies": {
     "documentation": "^4.0.0-beta.18",
-    "mastarm": "^5.1.2",
+    "es6-math": "^1.0.0",
+    "mastarm": "https://github.com/conveyal/mastarm/#8fa45b8c22594adfd2aa66d529a1b57904a8cbee",
     "nock": "^9.0.9",
     "react": "^15.4.2",
     "react-dom": "^15.4.2",