Merge pull request grpc#1756 from grpc/jcanizales-update-objc-instruc…

…tions

Add simpler instructions for ObjC (using Homebrew)

Merge pull request grpc#1218 from tbetbetbe/grpc_ruby_release_0_6_0

Bump ruby version to match the new release

Merge pull request grpc#827 from a11r/d2

Minor fix to INSTALL