wakatime 2.1.6 (new formula)

Adding new formula for wakatime
I'm not sure... it installs but afterwards I get this error when running it:

```
$ brew install wakatime
...
byte-compiling /usr/local/Cellar/wakatime/2.1.6/libexec/lib/python2.7/site-packages/wakatime/stats.py to stats.pyc
running install_egg_info
Copying wakatime.egg-info to /usr/local/Cellar/wakatime/2.1.6/libexec/lib/python2.7/site-packages/wakatime-2.1.6-py2.7.egg-info
running install_scripts
Installing wakatime script to /usr/local/Cellar/wakatime/2.1.6/libexec/bin
writing list of installed files to 'installed.txt'
🍺  /usr/local/Cellar/wakatime/2.1.6: 463 files, 10M, built in 2 seconds
$ wakatime
Traceback (most recent call last):
  File "/usr/local/bin/wakatime", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2793, in <module>
    working_set.require(__requires__)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 673, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 576, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: wakatime==2.1.6
```