Change iOS test target to 4.2

Target iphonesimulator6 or 5 aren't on the bots.
Review URL: https://codereview.chromium.org/14934006/

Patch from Justin Cohen <justincohen@google.com>!


git-svn-id: http://gyp.googlecode.com/svn/trunk@1631 78cadc50-ecff-11dd-a971-7dbc132099af