Force GPM::getUpdates call to json extension, in order to properly get back JSON response in case of error (#980)

CHANGELOG.md

@@ -4,6 +4,7 @@
 1. [](#bugfix)
     * Fix issue with validating page when switching language [#963](https://github.com/getgrav/grav-plugin-admin/issues/963)
     * Fix issue with quotes in Admin strings used in JS [#965](https://github.com/getgrav/grav-plugin-admin/issues/965)
+    * Force GPM::getUpdates call to json extension, in order to properly get back JSON response in case of error [#980](https://github.com/getgrav/grav-plugin-admin/issues/980)
 
 # v1.2.12
 ## 02/12/2017

themes/grav/app/utils/gpm.js

@@ -35,7 +35,7 @@ export default class GPM extends EventEmitter {
 
         this.emit('fetching', this);
 
-        fetch(config.base_url_relative, {
+        fetch(`${config.base_url_relative}.json`, {
             credentials: 'same-origin',
             method: 'post',
             body: data