Merge pull request #5050 from lucidsoftware/lucid

Change deprecated Bazel single file attr param

protobuf.bzl

@@ -178,7 +178,7 @@ proto_gen = rule(
         "protoc": attr.label(
             cfg = "host",
             executable = True,
-            single_file = True,
+            allow_single_file = True,
             mandatory = True,
         ),
         "plugin": attr.label(