Fix typo and broken "Hg.__init__" in 'hg' module

Fixes https://github.com/ansible/ansible/issues/4430 
- typo in line 237: 'module.parames[...]' should be 'module.params[...]'

While testing my change, I discovered another error in line 127:
- 'self.hg_path = self.hg_path' should read from the args to __init__ instead.

My first pull request - please excuse the whitespace changes.