Stringify error messages for Sentry

app/assets/javascripts/editor/ajax.js

@@ -12,6 +12,6 @@ CodeOceanEditorAJAX = {
     $.flash.danger({
       text: message.length > 0 ? message : $('#flash').data('message-failure')
     });
-    Sentry.captureException(response);
+    Sentry.captureException(JSON.stringify(response));
   }
 };

app/assets/javascripts/editor/editor.js.erb

@@ -572,7 +572,7 @@ configureEditors: function () {
         icon: ['fa', 'fa-bug'],
         text: $('#run').data('message-failure')
       });
-      Sentry.captureException(output);
+      Sentry.captureException(JSON.stringify(output));
     }
   },
 
@@ -622,7 +622,7 @@ configureEditors: function () {
     $.flash.danger({
       text: $('#flash').data('message-failure')
     });
-    Sentry.captureException(error);
+    Sentry.captureException(JSON.stringify(error));
   },
 
   showFileDialog: function(event) {

app/assets/javascripts/exercises.js.erb

@@ -112,7 +112,7 @@ $(document).on('turbolinks:load', function() {
     $.flash.danger({
       text: $('#flash').data('message-failure')
     });
-    Sentry.captureException(error);
+    Sentry.captureException(JSON.stringify(error));
   };
 
   var buildCheckboxes = function() {