Cleanup bump-version tests

[jhrcek]

The tests for bump-version command are slower compared to other tests (each taking ~7s on my pc). In my opinion it doesn't make sense to have so many end2end tests checking this functionality.
I think we should reduce these tests to maybe 1-2 end2end tests (using spago cli directly) and the rest should be deleted and replaced by unit/property tests of getNextVersion. WDYT?

[f-f]

@jhrcek sounds great! Faster tests are always nice 🙂

[jhrcek]

Here are just some numbers for referene:

Test suite duration as reported by Hspec Finished in X seconds, measured on my machine and averaged over 5 runs:
stack test: ~ 118 seconds
stack test --test-arguments '-m BumpVersion': ~ 69 seconds

So BumpVersion tests take about 57% time of the entire test suite.

[jhrcek]

Resolved in #445