Build fix: upb has namespaced bazel_version. (#431)

Fixes #430

Author: g-easy

WORKSPACE

@@ -57,7 +57,7 @@ apple_support_dependencies()
 
 load("@upb//bazel:repository_defs.bzl", "bazel_version_repository")
 
-bazel_version_repository(name = "bazel_version")
+bazel_version_repository(name = "upb_bazel_version")
 
 # Used by prometheus-cpp.
 local_repository(