Edit grammar in summary of 12.1.md
Edit grammar in summary of 12.1.md

WangKaimin/build-web-application-with-golang,faxriddin/build-web-application-with-golang,admpub/build-web-application-with-golang,WangKaimin/build-web-application-with-golang,songqii/build-web-application-with-golang,admpub/build-web-application-with-golang,admpub/build-web-application-with-golang,admpub/build-web-application-with-golang,astaxie/build-web-application-with-golang,astaxie/build-web-application-with-golang,faxriddin/build-web-application-with-golang,astaxie/build-web-application-with-golang,songqii/build-web-application-with-golang