message: update docstring in feature_csv_activation.py
  These changes in the test documentation reflect the changes introduced in
diff: @@ -9,8 +9,8 @@ BIP 68 - nSequence relative lock times
  BIP 112 - CHECKSEQUENCEVERIFY
  BIP 113 - MedianTimePast semantics for nLockTime
  -mine 82 blocks whose coinbases will be used to generate inputs for our tests
  -mine 345 blocks and seed block chain with the 82 inputs will use for our tests at height 427
  +mine 83 blocks whose coinbases will be used to generate inputs for our tests
  +mine 344 blocks and seed block chain with the 83 inputs used for our tests at height 427
  mine 2 blocks and verify soft fork not yet activated
  mine 1 block and test that soft fork is activated (rules enforced for next block)
  Test BIP 113 is enforced
  