Pip install broken

[cserby]

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.

[johanbrandhorst]

See issue #27