Use JSON when POSTing data

src/controllers/dashboard/encodingsettings.js

@@ -45,10 +45,10 @@ import libraryMenu from 'libraryMenu';
             return ApiClient.ajax({
                 url: ApiClient.getUrl('System/MediaEncoder/Path'),
                 type: 'POST',
-                data: {
+                data: JSON.stringify({
                     Path: form.querySelector('.txtEncoderPath').value,
                     PathType: 'Custom'
-                }
+                })
             }).then(Dashboard.processServerConfigurationUpdateResult, onSaveEncodingPathFailure);
         });
     }