doc/go1.4: mention that we are going to need a new version of SWIG
doc/go1.4: mention that we are going to need a new version of SWIG

Update issue 8750

CC=golang-codereviews
https://codereview.appspot.com/153950044

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go