Fix code block in "API Shape" section.

Bug: none
Change-Id: Id75500ca8b83d211e2b5c3a786e92f030791aedc
Reviewed-on: https://chromium-review.googlesource.com/726855Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510027}

services/api_standards.md

@@ -62,6 +62,7 @@ Below we outline concrete standards that aid in achieving the above goals.
   malevolent) client calling methods on a partially-constructed Foo. To be
   concrete:
 
+    ````
     // NO: Client will have access to partially-constructed Foo.
     interface Foo {
       SetClient(FooClient client);
@@ -73,6 +74,7 @@ Below we outline concrete standards that aid in achieving the above goals.
       GetFoo(Foo& request, FooClient client);
     };
     interface Foo { ... };
+    ````
 
 * In the absence of specific guidance, strive for consistency with surrounding
   interfaces and with interfaces in other services.