fix typo in example
fix typo in example

R=dsymonds
http://codereview.appspot.com/1715056

fuchsia-mirror/third_party-github.com-golang-protobuf,tamird/protobuf-2,skyportsystems/go-protobuf,skyportsystems/go-protobuf,jmptrader/protobuf-1,ArtemTeleshev/go-protobuf,jeremyletang/protobuf,golang/protobuf,mwitkow-io/protobuf,eduardiazf/protobuf,csuideal/protobuf,adnaan/protobuf,velocity-toolkit/protobuf-1,qinlodestar/protobuf,kung-foo/protobuf,trdata/protobuf,trdata/protobuf,jrbarron/protobuf,ekle/protoc-gen-goweb_test,tamird/protobuf-2,aoeu/protobuf,hailocab/protobuf,alskjstl/protobuf,ekle/protoc-gen-goweb,golang/protobuf,daemonl/protobuf,francoishill/protobuf,fuchsia-mirror/third_party-github.com-golang-protobuf,linkedin-inc/protobuf