Bump Python version

build.yaml

@@ -7,6 +7,7 @@ settings:
   '#3': Use "-preN" suffixes to identify pre-release versions
   '#4': Per-language overrides are possible with (eg) ruby_version tag here
   '#5': See the expand_version.py for all the quirks here
+  python_version: 0.13.0-pre2
   ruby_version: 0.13.0-pre1.1
   version: 0.13.0-pre1
 filegroups:

src/python/grpcio/grpc_version.py

@@ -29,4 +29,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio/grpc_version.py.template`!!!
 
-VERSION='0.13.0rc1'
+VERSION='0.13.0rc2'