Add proper polyfill for IE11

Signed-off-by: Julius Härtl <jus@bitgrid.net>

js/package.json

@@ -8,16 +8,17 @@
     "test": "tests"
   },
   "dependencies": {
+    "@uirouter/angularjs": "^1.0.18",
     "angular": "^1.7.2",
     "angular-animate": "^1.7.2",
     "angular-file-upload": "^2.5.0",
     "angular-markdown-it": "^0.6.1",
     "angular-sanitize": "^1.7.2",
+    "babel-polyfill": "^6.26.0",
     "markdown-it": "^8.4.1",
     "markdown-it-link-target": "^1.0.2",
     "ng-sortable": "^1.3.8",
-    "ui-select": "^0.19.8",
-    "@uirouter/angularjs": "^1.0.18"
+    "ui-select": "^0.19.8"
   },
   "devDependencies": {
     "babel-core": "^6.26.0",