.travis.yml: all 0.2.40 builds use xcode10.1
.travis.yml: all 0.2.40 builds use xcode10.1

older xcode versions doesn't support pip3
and aws installation require it

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