Bump mypy_extensions version to 0.2.0-dev

setup.py

diff --git a/setup.py b/setup.py
index b339a1e..3490840 100644
--- a/setup.py
+++ b/setup.py
@@ -4,7 +4,7 @@
 
 from distutils.core import setup
 
-version = '0.1.0'
+version = '0.2.0-dev'
 description = 'Experimental type system extensions for programs checked with the mypy typechecker.'
 long_description = '''
 Mypy Extensions