Tox cannot recognize interpreters on the form pythonx.x-sometexthere

[pablogsal]

The regular expression that tries to match interpreter versions in

https://github.com/tox-dev/tox/blob/master/src/tox/interpreters/py_spec.py#L56

should end in '$' as right know is stripping everything that ends if the interpreter starts with pythonx.x. The debug versions of the interpreters usually are in the form pythonx.x-dbg so is important to make this change as right know it will run with the non-debug version silently.