fix(ionicConfig): add content scheme to whitelist

When using the camera plugin, it will use a content:// scheme, which will be marked unsafe. Closes ionic-team#3719

js/angular/service/ionicConfig.js

@@ -629,5 +629,5 @@ IonicModule
 // running-cordova-apps-on-windows-and-windows-phone-8-1-using-ionic-angularjs-and-other-frameworks.aspx
 .config(['$compileProvider', function($compileProvider) {
   $compileProvider.aHrefSanitizationWhitelist(/^\s*(https?|tel|ftp|mailto|file|ghttps?|ms-appx|x-wmapp0):/);
-  $compileProvider.imgSrcSanitizationWhitelist(/^\s*(https?|ftp|file|blob|ms-appx|x-wmapp0):|data:image\//);
+  $compileProvider.imgSrcSanitizationWhitelist(/^\s*(https?|ftp|file|content|blob|ms-appx|x-wmapp0):|data:image\//);
 }]);