Fix link to the 2.0 upgrade guide in the README
Fix link to the 2.0 upgrade guide in the README

Now that the `swift-2.0` branch has been merged and deleted the migration guide is located on the `master` branch.
suxinde2009/Alamofire,Baza207/Alamofire,thebugcode/Alamofire,suxinde2009/Alamofire,leelili/Alamofire,Swiftosis/Alamofire,Alamofire/Alamofire,sarunw/Alamofire,kiancheong/Alamofire,sarunw/Alamofire,youweit/Alamofire,brandenr/Alamofire,Baza207/Alamofire,rain1988/Alamofire,foxkillerli/Alamofire,mcgrady20150318/Alamofire,DreamHill/Alamofire,libiao88/Alamofire,lclamotte/Alamofire,revdotcom/Alamofire,Noobish1/Alamofire,twobitlabs/Alamofire,trauzti/Alamofire,easyui/Alamofire,i-miss-you/Alamofire,bscarano/Alamofire,jschmid/Alamofire,gauravds/Alamofire,liuchungui/Alamofire,BNakum/Alamofire,rafaelvg/Alamofire,jmkr/Alamofire,dandalf/Alamofire,Holmusk/Alamofire,st3fan/Alamofire,Vkt0r/Alamofire,nickygerritsen/Alamofire,alvincrisuy/Alamofire,rain1988/Alamofire,PhilJay/Alamofire,red3/Alamofire,dawangjiaowolaixunshan/Alamofire,trauzti/Alamofire,cesar-oyarzun-m/Alamofire,irealme/Alamofire,Staance/Alamofire,ThornTechPublic/Alamofire,davepatterson/Alamofire,Holmusk/Alamofire,Karumi/Alamofire-Result,yimajo/Alamofire,Alamofire/Alamofire,Koalappp/Alamofire,dandalf/Alamofire,john-langley/Alamofire,yaoxiaoyong/Alamofire,LionHeart123/Alamofire,dawangjiaowolaixunshan/Alamofire,BNakum/Alamofire,rafaelvg/Alamofire,agustindc-rga/Alamofire,nickygerritsen/Alamofire,Paul-van-Klaveren/Alamofire,followwind007/Alamofire,robskillington/Alamofire,tokorom/Alamofire,neugartf/Alamofire,rjsamson/Alamofire,Lomotif/Alamofire,chokett/Alamofire,meteochu/Alamofire,revdotcom/Alamofire,petereddy/Alamofire,neugartf/Alamofire,libiao88/Alamofire,Karumi/Alamofire-Result,richardPFisk/Alamofire,PhuocLinh/Alamofire,Farteen/Alamofire,MaWenxing/Alamofire,leelili/Alamofire,antigp/Alamofire,petereddy/Alamofire,irealme/Alamofire,davepatterson/Alamofire,christophercotton/Alamofire,yujiaao/Alamofire,zuthan/Alamofire,mbhuta/Alamofire,kevin-zqw/Alamofire,Paul-van-Klaveren/Alamofire,chokett/Alamofire,alvincrisuy/Alamofire,mcgrady20150318/Alamofire,ThornTechPublic/Alamofire,antigp/Alamofire,dgdosen/Alamofire,PhilJay/Alamofire,androidrivne/Alamofire,DouKing/Alamofire,yaoxiaoyong/Alamofire,ikesyo/Alamofire,Koalappp/Alamofire,DouKing/Alamofire,cmpt275group9/Alamofire,iosheadhunter/Alamofire,sai43/Alamofire,DreamHill/Alamofire,tonyli508/AlamofireDomain,dgdosen/Alamofire,Staance/Alamofire,bscarano/Alamofire,AnthonyMDev/Alamofire,muukii/Alamofire,Farteen/Alamofire,meteochu/Alamofire,AnthonyMDev/Alamofire,muukii/Alamofire,robskillington/Alamofire,zuthan/Alamofire,followwind007/Alamofire,rjsamson/Alamofire,jschmid/Alamofire,yujiaao/Alamofire,yjkim/Alamofire,richardPFisk/Alamofire,MaWenxing/Alamofire,youweit/Alamofire,jmkr/Alamofire,SampleLiao/Alamofire,guipanizzon/Alamofire,kevin-zqw/Alamofire,tokorom/Alamofire,john-langley/Alamofire,hazytint/Alamofire,Lomotif/Alamofire,guipanizzon/Alamofire,Screon/Alamofire,RyanCodes/Alamofire,gauravds/Alamofire,agustindc-rga/Alamofire,androidrivne/Alamofire,thebugcode/Alamofire,RyanCodes/Alamofire,foxkillerli/Alamofire,yjkim/Alamofire,ikesyo/Alamofire,Vkt0r/Alamofire,kiancheong/Alamofire,red3/Alamofire,liuchungui/Alamofire,tonyli508/AlamofireDomain,LionHeart123/Alamofire,yimajo/Alamofire,lclamotte/Alamofire,brandenr/Alamofire,hazytint/Alamofire,mbhuta/Alamofire,cesar-oyarzun-m/Alamofire,cmpt275group9/Alamofire,Holmusk/Alamofire,Noobish1/Alamofire,christophercotton/Alamofire,easyui/Alamofire,ernestopino/Alamofire,bnadim/Alamofire,alex-learn/Alamofire,sai43/Alamofire,Swiftosis/Alamofire,bnadim/Alamofire,Screon/Alamofire,twobitlabs/Alamofire,st3fan/Alamofire,PhuocLinh/Alamofire,i-miss-you/Alamofire,ernestopino/Alamofire,SampleLiao/Alamofire,iosheadhunter/Alamofire,alex-learn/Alamofire