Bump protobuf for Bazel 0.21 (#1493)

Protobuf 3.5 would require a Bazel flag
bazel build --incompatible_package_name_is_a_function=false
for Bazel 0.21 because its bazel syntax is old.
Rather than building with this flag, let's just update
the protobuf version.

Also, fix lint.

bazel/repositories.bzl

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 """External dependencies for Cartographer."""
+
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 def cartographer_repositories():
@@ -206,11 +207,11 @@ def cartographer_repositories():
     _maybe(
         http_archive,
         name = "com_google_protobuf",
-        sha256 = "0cc6607e2daa675101e9b7398a436f09167dffb8ca0489b0307ff7260498c13c",
-        strip_prefix = "protobuf-3.5.0",
+        sha256 = "2244b0308846bb22b4ff0bcc675e99290ff9f1115553ae9671eba1030af31bc0",
+        strip_prefix = "protobuf-3.6.1.2",
         urls = [
-            "https://mirror.bazel.build/github.com/google/protobuf/archive/v3.5.0.tar.gz",
-            "https://github.com/google/protobuf/archive/v3.5.0.tar.gz",
+            "https://mirror.bazel.build/github.com/google/protobuf/archive/v3.6.1.2.tar.gz",
+            "https://github.com/google/protobuf/archive/v3.6.1.2.tar.gz",
         ],
     )
 
@@ -247,7 +248,8 @@ def cartographer_repositories():
         ],
     )
 
-    _maybe(http_archive,
+    _maybe(
+        http_archive,
         name = "com_github_googlecartographer_async_grpc",
         sha256 = "83c2a27c92979787f38810adc4b6bb67aa09607c53dbadca3430a5f29e0a1cd3",
         strip_prefix = "async_grpc-771af45374af7f7bfc3b622ed7efbe29a4aba403",
@@ -256,7 +258,8 @@ def cartographer_repositories():
         ],
     )
 
-    _maybe(http_archive,
+    _maybe(
+        http_archive,
         name = "com_google_absl",
         sha256 = "c8ba586a9ab12bc4a67bb419fc0d2146200942b072bac95f50490f977b7fb04f",
         strip_prefix = "abseil-cpp-5441bbe1db5d0f2ca24b5b60166367b0966790af",