Execute tests on Mono

https://github.com/codingteam/naggum/blob/96eae4f9eadcf9b0ce257cc28098bbd60fdb8bb1/Naggum.Test/Process.fs#L6

Currently it somehow works, but I fear that we need to detect mono and run these executables with `mono` prepended to them. Need to either change that code or find a documentation about executable resolve details when running on Mono.
