Update WORKSPACE / BUILD to work with bazel at HEAD.

Uses external rules_go github repository.

submodule/BUILD

@@ -1,21 +1,21 @@
-load("@bazel_tools//tools/build_rules/go:def.bzl", "go_prefix", "go_binary")
+load("@io_bazel_rules_go//go:def.bzl", "go_binary")
 
 package(
     default_visibility = ["//visibility:public"],
 )
 
 go_binary(
-	name ="bare",
-	srcs = [ "bare.go" ],
-	deps = [
-	    "//submodule/src:bare",
-	],
+    name = "bare",
+    srcs = ["bare.go"],
+    deps = [
+        "//submodule/src:bare",
+    ],
 )
 
 go_binary(
-	name ="remote",
-	srcs = [ "remote.go" ],
-	deps = [
-	    "//submodule/src/remote",
-	],
+    name = "remote",
+    srcs = ["remote.go"],
+    deps = [
+        "//submodule/src/remote",
+    ],
 )