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: Id8bd40142965c2f9fa8f656c5c8cdee1d3eddba0

bazlets.bzl

diff --git a/bazlets.bzl b/bazlets.bzl
index f97b72c..f089af4 100644
--- a/bazlets.bzl
+++ b/bazlets.bzl
@@ -1,10 +1,12 @@
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
+
 NAME = "com_googlesource_gerrit_bazlets"
 
 def load_bazlets(
         commit,
         local_path = None):
     if not local_path:
-        native.git_repository(
+        git_repository(
             name = NAME,
             remote = "https://gerrit.googlesource.com/bazlets",
             commit = commit,