increment version to 0.4.0 (#291)

Summary:
Pull Request resolved: #291

Incrementing version number in anticipation of new release

Reviewed By: Eric-Cortez

Differential Revision: D46366166

fbshipit-source-id: 8b93cee1a781a5c06d205480c1d152abba0020c7

Author: crasanders

aepsych/version.py

@@ -5,4 +5,4 @@
 # This source code is licensed under the license found in the
 # LICENSE file in the root directory of this source tree.
 
-__version__ = "0.4.0dev"
+__version__ = "0.4.0"