app/build: add android to first-class ports list
app/build: add android to first-class ports list

I cannot work out how to test this. I tried "goapp serve" but the local
instance says "tag not found".

Change-Id: I1f2585277e5a114753000901f22d6d1adba06611
Reviewed-on: https://go-review.googlesource.com/5050
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

evandbrown/build,proppy/build,golang/build,proppy/build,evandbrown/build,golang/build,proppy/build,golang/build,golang/build,evandbrown/build,proppy/build