Update minimum bazel version to 0.13.0.

I was using bazel 0.12.0 and was getting the error:

file '@bazel_tools//tools/cpp:windows_cc_configure.bzl' does not contain symbol 'setup_vc_env_vars'

PiperOrigin-RevId: 205316270
diff --git a/WORKSPACE b/WORKSPACE
index fd7570a..e7cf23a 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -18,7 +18,7 @@
 # files, in case the parsing of those build files depends on the bazel
 # version we require here.
 load("//tensorflow:version_check.bzl", "check_bazel_version_at_least")
-check_bazel_version_at_least("0.10.0")
+check_bazel_version_at_least("0.13.0")
 
 load("//tensorflow:workspace.bzl", "tf_workspace")