Fix grammar and translations for section "Introduction to seelog" in 12.1.md
Fix grammar and translations for section "Introduction to seelog" in
12.1.md

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