Merge pull request tensorflow#2372 from kevinrobinson/master

Typo fix for comment in worker.proto

Author: caisq

tensorflow/core/protobuf/worker.proto

@@ -154,7 +154,7 @@ message RunGraphRequest {
 
   // A unique ID to distinguish different runs of the same graph.
   //
-  // The master generates a global unique `step_id` to dinstinguish
+  // The master generates a global unique `step_id` to distinguish
   // different runs of the graph computation. Subgraphs communicate
   // (e.g., send/recv ops) with each other using `step_id` to
   // distinguish tensors generated by different runs.