BUG - Module capitalization in aa_example_helloworld_model 

The module aamod_biascorrect_meanEPI is referenced, whereas the actual xml file in aa_modules is aamod_biascorrect_meanepi.xml. This gives an error. Proposed: Fix capitalization.

https://github.com/automaticanalysis/automaticanalysis/discussions/254#discussioncomment-1471279