Drupal GMap module: Mixed content with markerclusterer.js or markerclusterer_packed.js

Drupal GMap module (in our case Version: 7.x-2.9) might cause the following mixed-content warning with HTTPS:

http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclu...

Solution: Edit markerclusterer.js or markerclusterer_packed.js and change

http|utility|library|v3|googlecode|com|svn|trunk|markerclusterer|images|png|

to:

https|utility|library|v3|googlecode|com|svn|trunk|markerclusterer|images|png|

See also:
https://stackoverflow.com/questions/37087583/google-maps-not-working-in-...
https://stackoverflow.com/questions/37180731/what-is-the-alternate-sourc...