bazlets: Replace native.git_repository with skylark rule

The native.git_repository rule does not work properly when invoked
in a `git submodule foreach` command. Bazel will deprecate the
native rules anyway, so replace with skylark's git_repository.

See [1] for context.

[1] https://github.com/bazelbuild/bazel/issues/6358#issuecomment-429103745

Change-Id: Ib9efda267c5545f73fcbacbf7ac4ffcfd28d3216

bazlets.bzl

diff --git a/bazlets.bzl b/bazlets.bzl
index e14e488..6c4fffc 100644
--- a/bazlets.bzl
+++ b/bazlets.bzl
@@ -1,3 +1,5 @@
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
+
 NAME = "com_googlesource_gerrit_bazlets"
 
 def load_bazlets(
@@ -5,7 +7,7 @@
     local_path = None
   ):
   if not local_path:
-      native.git_repository(
+      git_repository(
           name = NAME,
           remote = "https://gerrit.googlesource.com/bazlets",
           commit = commit,