Fix typo in Mojom grammer reference.

Change-Id: I24e2ce9d712e2d5d1c2fb619216395aa6cf7a1be
Reviewed-on: https://chromium-review.googlesource.com/c/1490369
Auto-Submit: Owen Rodley <orodley@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#635885}

mojo/public/tools/bindings/README.md

@@ -713,7 +713,7 @@ StructBody = <empty>
            | StructBody Const
            | StructBody Enum
            | StructBody StructField
-StructField = AttributeSection TypeSpec Name Orginal Default ";"
+StructField = AttributeSection TypeSpec Name Ordinal Default ";"
 
 Union = AttributeSection "union" Name "{" UnionBody "}" ";"
 UnionBody = <empty> | UnionBody UnionField