Increment package ver. Only trainers were changed.

Author: Ervin Teng

ml-agents/setup.py

@@ -10,7 +10,7 @@
 
 setup(
     name="mlagents",
-    version="0.9.0",
+    version="0.9.0a",
     description="Unity Machine Learning Agents",
     long_description=long_description,
     long_description_content_type="text/markdown",