Make buildtools compatible with future releases of Bazel (#771)

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index a2bbbfb..4acd0db 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -5,30 +5,55 @@
 http_archive(
     name = "io_bazel_rules_go",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/0.18.5/rules_go-0.18.5.tar.gz",
-        "https://github.com/bazelbuild/rules_go/releases/download/0.18.5/rules_go-0.18.5.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.21.0/rules_go-v0.21.0.tar.gz",
+        "https://github.com/bazelbuild/rules_go/releases/download/v0.21.0/rules_go-v0.21.0.tar.gz",
     ],
-    sha256 = "a82a352bffae6bee4e95f68a8d80a70e87f42c4741e6a448bec11998fcc82329",
+    sha256 = "b27e55d2dcc9e6020e17614ae6e0374818a3e3ce6f2024036e688ada24110444",
 )
-http_archive(
-    name = "bazel_gazelle",
-    urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/bazel-gazelle/releases/download/0.17.0/bazel-gazelle-0.17.0.tar.gz",
-        "https://github.com/bazelbuild/bazel-gazelle/releases/download/0.17.0/bazel-gazelle-0.17.0.tar.gz",
-    ],
-    sha256 = "3c681998538231a2d24d0c07ed5a7658cb72bfb5fd4bf9911157c0e9ac6a2687",
-)
+
 load("@io_bazel_rules_go//go:deps.bzl", "go_rules_dependencies", "go_register_toolchains")
 go_rules_dependencies()
 go_register_toolchains()
+
+http_archive(
+    name = "bazel_gazelle",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-gazelle/releases/download/v0.19.1/bazel-gazelle-v0.19.1.tar.gz",
+        "https://github.com/bazelbuild/bazel-gazelle/releases/download/v0.19.1/bazel-gazelle-v0.19.1.tar.gz",
+    ],
+    sha256 = "86c6d481b3f7aedc1d60c1c211c6f76da282ae197c3b3160f54bd3a8f847896f",
+)
 load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies", "go_repository")
 gazelle_dependencies()
-
-load("@com_github_bazelbuild_buildtools//buildifier:deps.bzl", "buildifier_dependencies")
-buildifier_dependencies()
-
 go_repository(
     name = "skylark_syntax",
     commit = "fc7a7f44baedf13df916b2aad597bc944964dd27",
     importpath = "go.starlark.net",
 )
+
+http_archive(
+    name = "com_google_protobuf",
+    strip_prefix = "protobuf-3.11.2",
+    urls = [
+        "https://github.com/protocolbuffers/protobuf/archive/v3.11.2.tar.gz",
+    ],
+    sha256 = "e8c7601439dbd4489fe5069c33d374804990a56c2f710e00227ee5d8fd650e67",
+)
+load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
+protobuf_deps()
+
+http_archive(
+    name = "rules_proto",
+    sha256 = "602e7161d9195e50246177e7c55b2f39950a9cf7366f74ed5f22fd45750cd208",
+    strip_prefix = "rules_proto-97d8af4dc474595af3900dd85cb3a29ad28cc313",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_proto/archive/97d8af4dc474595af3900dd85cb3a29ad28cc313.tar.gz",
+        "https://github.com/bazelbuild/rules_proto/archive/97d8af4dc474595af3900dd85cb3a29ad28cc313.tar.gz",
+    ],
+)
+load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies", "rules_proto_toolchains")
+rules_proto_dependencies()
+rules_proto_toolchains()
+
+load("@com_github_bazelbuild_buildtools//buildifier:deps.bzl", "buildifier_dependencies")
+buildifier_dependencies()