Specify min required bazel version

If bazel is too old fail build early with a precise error message.
Idea taken from [1].

[1] https://github.com/bazelbuild/bazel/commit/6c2aaacb5b9b01fa5614b6a2b147859fc70c9125

Change-Id: I5dafd1ab7b88caa19707b68d4a07c3b9ab9005cf
diff --git a/WORKSPACE b/WORKSPACE
index 6458571..e7c26ab 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -1,5 +1,9 @@
 workspace(name = "gerrit")
 
+load("//:version.bzl", "check_version")
+
+check_version("0.5.3")
+
 load("//tools/bzl:maven_jar.bzl", "maven_jar", "GERRIT", "MAVEN_LOCAL")
 load("//lib/codemirror:cm.bzl", "CM_VERSION", "DIFF_MATCH_PATCH_VERSION")
 load("//plugins:external_plugin_deps.bzl", "external_plugin_deps")