Typo correction

Change Receiver_ to receiver_ to match the initialization from constructor

Change-Id: Ibe26bcc9333c9b8bac7a9e687ca5814d9453ca95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1782967
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Charlie Hu <chenleihu@google.com>
Cr-Commit-Position: refs/heads/master@{#703876}

docs/mojo_and_services.md

@@ -186,7 +186,7 @@ class PingResponderImpl : example::mojom::PingResponder {
   }
 
  private:
-  mojo::Receiver<example::mojom::PingResponder> Receiver_;
+  mojo::Receiver<example::mojom::PingResponder> receiver_;
 
   DISALLOW_COPY_AND_ASSIGN(PingResponderImpl);
 };