Typo in README file
Typo in README file

Voiceworks/SIP.js,vconsult/JsSIP,onsip/SIP.js,markandrus/SIP.js,dpocock/JsSIP,DrumTechnologiesLtd/JsSIP,onsip/SIP.js,joseph-onsip/SIP.js,tqcenglish/JsSIP,voxbone/JsSIP,josephfrazier/SIP.js,CodeYellowBV/JsSIP,Escaux/SIP.js,AaronZhangL/JsSIP,rusekr/JsSIP,ronlobo/SIP.js