Add bazelbuild/rules_proto to downstream projects (#798)

The pipeline has been green for some time now :) https://buildkite.com/bazel/rules-proto
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index 873fada..8db1396 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -323,6 +323,11 @@
         "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_perl/master/.bazelci/presubmit.yml",
         "pipeline_slug": "rules-perl",
     },
+    "rules_proto": {
+        "git_repository": "https://github.com/bazelbuild/rules_proto.git",
+        "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_proto/master/.bazelci/presubmit.yml",
+        "pipeline_slug": "rules-proto",
+    },
     "rules_python": {
         "git_repository": "https://github.com/bazelbuild/rules_python.git",
         "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_python/master/.bazelci/presubmit.yml",