Hotfix examples

This MR implements a couple of straightforward fixes to the examples.

1. Update the RMSProp-implementation example, based on the recent API changes (see MR !9 (merged)).
2. Fix a default argparse parameter in the server-side script of the Heart UCI example.

Note that there is a current effort to improve and diversify the examples, which has addressed point 2; however they might take a bit of time to finish up, hence this hotfix that prevents current demos from failing.