Environment variable for custom location of the python executable

My python isn't installed in c:\python27. So i added an environemtn variable named HUBOT_SKYPE_ADAPTER_PYTHON.

Usage: 
```
set HUBOT_SKYPE_ADAPTER_PYTHON=D:\Tools\Python27\python.exe
node .\node_modules\coffee-script\bin\coffee .\bin\hubot -a skype
```