Fix a typo in a plain scalar scanner.
Fix a typo in a plain scalar scanner.

anishathalye/pyyaml,yaml/pyyaml,yaml/pyyaml,anishathalye/pyyaml,jamesbroadhead/pyyaml,jamesbroadhead/pyyaml,yaml/pyyaml,fuchsia-mirror/third_party-pyyaml,fuchsia-mirror/third_party-pyyaml