cleanup: Fix missing/stray spaces

Those are wrong according to our style guidelines, but the previous
eslint ruleset didn't catch them.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/805

js/misc/loginManager.js

@@ -103,7 +103,7 @@ var LoginManagerSystemd = class {
 
     getCurrentSessionProxy(callback) {
         if (this._currentSession) {
-            callback (this._currentSession);
+            callback(this._currentSession);
             return;
         }