marker clustered mashup is not working anymore on google.

A temporary solution is pretty easy, you have already found most of it.
As a workaround (at least until Pronamic releases a new version), go to /wp-content/plugins/pronamic-google-maps/assets/google-maps-marker-clusterer-plus/ folder and edit markercluster.js and markercluster.min.js by replacing the string

MarkerClusterer.IMAGE_PATH = “https://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclustererplus/images/m”;

with

MarkerClusterer.IMAGE_PATH = “https://cdn.rawgit.com/googlemaps/js-marker-clusterer/gh-pages/images/m”;

Yup, I noticed this too. Aparently the move to github took place 2 years ago already.

This was fixed in https://github.com/pronamic/wp-pronamic-google-maps/commit/704ef2a54b614750cbe04bdb607a85dcac781cf4.