add es6.map to the ie11-polyfill

so we can use Map properly in the canvas planner

refs FALCOR-224

test plan:
* automated tests pass

Change-Id: I444c963b5094372a82dbef16479ff7e442127d52
Reviewed-on: https://gerrit.instructure.com/113281
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Tested-by: Jenkins
Product-Review: Jon Willesen <jonw+gerrit@instructure.com>
QA-Review: Jon Willesen <jonw+gerrit@instructure.com>

gulpfile.js

@@ -117,7 +117,8 @@ function makeIE11Polyfill () {
     'es6.string.ends-with',
     'es6.string.includes',
     'es6.string.starts-with',
-    'es6.symbol'
+    'es6.symbol',
+    'es6.map'
   ]
 
   return coreJsBuilder({