Update Prerelease Tag to RC3
Update Prerelease Tag to RC3

Since we have branched for RC2, we should use a different pre-release
tag for builds out of ProjectK/master.

[tfs-changeset: 1566436]

dotnet/wcf,iamjasonp/wcf,khdang/wcf,dotnet/wcf,StephenBonikowsky/wcf,imcarolwang/wcf,ElJerry/wcf,imcarolwang/wcf,dotnet/wcf,shmao/wcf,mconnew/wcf,hongdai/wcf,ericstj/wcf,KKhurin/wcf,hongdai/wcf,ElJerry/wcf,MattGal/wcf,iamjasonp/wcf,zhenlan/wcf,khdang/wcf,StephenBonikowsky/wcf,shmao/wcf,KKhurin/wcf,imcarolwang/wcf,ericstj/wcf,mconnew/wcf,mconnew/wcf,MattGal/wcf,zhenlan/wcf