Upgrade bazel to 0.15.0.

PiperOrigin-RevId: 205878953
diff --git a/configure.py b/configure.py
index 1df7bc7..f97bf8a 100644
--- a/configure.py
+++ b/configure.py
@@ -1451,7 +1451,7 @@
   # environment variables.
   environ_cp = dict(os.environ)
 
-  check_bazel_version('0.13.0')
+  check_bazel_version('0.15.0')
 
   reset_tf_configure_bazelrc(args.workspace)
   cleanup_makefile()