Release 1.2.1

Whoups, I released the 1.2.0 tag on github and then realized I had
forgot to update this setup.py file.

Note to self: I think the order to release is

 * (i) Update version number in setup.py
 * (ii) pypi (Executing `python setup.py sdist upload`)
 * (iii) Add tag on github (https://github.com/spotify/luigi/releases)
 * (iv) Then bump setup.py, "preparing for next release".

setup.py

@@ -55,7 +55,7 @@ def get_static_files(path):
 
 setup(
     name='luigi',
-    version='1.1.3',
+    version='1.2.1',
     description='Workflow mgmgt + task scheduling + dependency resolution',
     long_description=long_description,
     author='Erik Bernhardsson',