Added cross-compiler to $PATH in continuous-build.sh
and enabled sudo in .travis.yml.
NOTES:
- travis is unable to update submodules pointing to commits out of their master branch,
so if you push to devtools, you need to push into master branch or your build will be broken
- travis caches conflicts with submodule managements, so we use tmp/toolchain instead of
hacking/cross/toolchain in .travis.yml and continuous-build.sh will mv binaries as required.