Fixed tinymce5 changing image issue

In TinyMCE 5, when tring to select new image to replace exist one the function usingTinymce4AndColorbox() returns TRUE (False Positive).
The bug is preventing from changing the existing image.
I fixed it with extra check to insure usingTinymce4AndColorbox() is returning FALSE when TinyMCE 5 is active.

Author: Generation4

public/js/script.js

@@ -760,7 +760,7 @@ function usingTinymce3() {
 }
 
 function usingTinymce4AndColorbox() {
-  return !!getUrlParam('field_name');
+  return !!getUrlParam('field_name') && getUrlParam('editor') != 'tinymce5';
 }
 
 function usingTinymce5(){