Extend 'makePDF.py' to also accept the file extension '.tikz'. It is now...

... easy to extend the list of accepted file extensions by simply extending the string.

The motivation for this is that I also want to compile TikZ code that is generated from "matlab2tikz". Those files need to have the extension ".tikz" because I also include them in my main latex file using the CTAN package "tikzscale".

This is my first pull request. Suggestions how I should improve the process are highly welcome!