Bug 1532284 - Build using android-28. r=gw
Bug 1532284 - Build using android-28. r=gw

This is the SDK version we use to build other Android stuff in
mozilla-central. It's simpler if we build Wrench using the same
target since we can reuse the toolchains.

Depends on D22376

Differential Revision: https://phabricator.services.mozilla.com/D22377

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/b958c752bbe677243668c83c3e6604867f8091f8

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender