Get emscripten from GitHub
Get emscripten from GitHub

The emsdk was being installed from an old mozilla-games URL.  This
clones from GitHub so Travis always tries to use the latest version.

hostilefork/rebol,draegtun/ren-c,draegtun/ren-c,rgchris/ren-c,draegtun/ren-c,giuliolunati/ren-c,rgchris/ren-c,giuliolunati/ren-c,hostilefork/rebol,draegtun/ren-c,rgchris/ren-c,hostilefork/rebol,giuliolunati/ren-c,rgchris/ren-c,hostilefork/rebol,draegtun/ren-c,rgchris/ren-c,giuliolunati/ren-c,hostilefork/rebol,hostilefork/rebol,giuliolunati/ren-c,draegtun/ren-c