Added HAXE_VER

 - Pre-built: latest (empty/unset), 3.1.3 and 3.1.2
 - Others: build from git
 - Missing dependencies for builds on Mac
Did you run into problems with $(dirname $0) ? I prefer using it instead of $PWD, because $PWD assumes that we're running from the same TRAVIS_HX dir, which may not be true (e.g. ~/travis-hx/setup.sh will fail)