Fix Travis failure

For travis tests, we host pre-built bundles of the arm-gcc and sdcc
toolchains on github, and we download them with curl

Apparently, the URL for those bundles has been changed and the
HTTP response is a 301 redirect. curl doesn't follow it

We change .travis.yml to pull the bundles form the new location
Merge pull request #662 from g-oikonomou/travis-url-fix

Fix Travis failure