Pip install broken

Currently it is not possible to install funcsigs using pip install.

The problem is caused by this line:
      extras_require = {

> > ```
> >      ':python_version<"2.7"': ['ordereddict'],
> >   },
> > ```

error in funcsigs setup command: Invalid environment marker: python_version<"2.7"

Please remove the extra colon from the start of the string.
