Increment minimal required FF version to 50 (#161)

Quickfix, as long as #76 is not yet implemented.

See #139 (comment)

src/app.ts

@@ -62,7 +62,7 @@ angular.module('3ema', [
 
 // Constants to be used by controllers
 .constant('BROWSER_MIN_VERSIONS', {
-    FF: 47,
+    FF: 50,
     CHROME: 45,
     OPERA: 32,
 })