Add periods and fix minor typos in API.md
Add periods and fix minor typos in API.md

skovhus/jest,securingsincity/jest-browser-support,alvinsj/jest,siddhartharay007/jest,silentroach/jest,securingsincity/jest-browser-support,sampepose/jest,ide/jest,aduyng/jest,dylanham/jest,mpontus/jest,mpontus/jest,bluebridgedigital/jest,bluebridgedigital/jest,skawian/jest,bookman25/jest,dylanham/jest,mpontus/jest,cpojer/jest,machadoum/jest,IveWong/jest,carmenlau/jest,skawian/jest,yungsters/jest,blainekasten/jest,aaron-goshine/jest,skovhus/jest,createbang/jest,machadoum/jest,BenoitZugmeyer/jest,wmyers/jest,ide/jest,AyseAkr/jest,jsdf/jest,ncuillery/jest,aduyng/jest,BenoitZugmeyer/jest,lokinell/jest,xeneta/jest,alvinsj/jest,blainekasten/jest,skovhus/jest,gagoman/jest,StatusPage/jest,facebook/jest,Daniel15/jest,bookman25/jest,lokinell/jest,rpowis/jest,cpojer/jest,silentroach/jest,jsdf/jest,carmenlau/jest,bauerca/jest,Daniel15/jest,createbang/jest,yungsters/jest,ChiMarvine/jest,cpojer/jest,IveWong/jest,gagoman/jest,xeneta/jest,razh/jest,Daniel15/jest,facebook/jest,facebook/jest,wmyers/jest,rpowis/jest,aaron-goshine/jest,sampepose/jest,blainekasten/jest,ChiMarvine/jest,ncuillery/jest,razh/jest,aaron-goshine/jest,securingsincity/jest-browser-support,ide/jest,siddhartharay007/jest,StatusPage/jest,bookman25/jest,bauerca/jest,AyseAkr/jest