AppImage has Travis-CI paths

[tresf]

The AppImage's AppRun has some paths added that are benign but shouldn't be there, probably due to improper immediate variable expansion.

Most of these are benign because they'll never exist on a machine, but some, such as /opt/qt59/bin can cause issues, since the AppImage should prefer the Qt5 that it ships with.

export PATH="\
/home/travis/build/PhysSong/lmms/build/cmake/linux/squashfs-root/usr/bin:\
/opt/qt59/bin:\
/opt/qt59/bin:\
/home/travis/.rvm/gems/ruby-2.4.1/bin:\
/home/travis/.rvm/gems/ruby-2.4.1@global/bin:\
/home/travis/.rvm/rubies/ruby-2.4.1/bin:\
/home/travis/.rvm/bin:\
/home/travis/bin:\
/home/travis/.local/bin:\
/opt/pyenv/shims:\
/home/travis/.phpenv/shims:\
/home/travis/perl5/perlbrew/bin:
/home/travis/.nvm/versions/node/v8.9.1/bin:\
/home/travis/.kiex/elixirs/elixir-1.4.5/bin:\
/home/travis/.kiex/bin:\
/home/travis/gopath/bin:/home/travis/.gimme/versions/go1.7.4.linux.amd64/bin:\
/usr/local/phantomjs/bin:/usr/local/phantomjs:\
/usr/local/neo4j-3.2.7/bin:/usr/local/maven-3.5.2/bin:/usr/local/cmake-3.9.2/bin:\
/usr/local/clang-5.0.0/bin:\
/usr/local/sbin:\
/usr/local/bin:\
/usr/sbin:/usr/bin:\
/sbin:\
/bin:\
/home/travis/.phpenv/bin:\
/opt/pyenv/bin:\
/home/travis/.yarn/bin:\
/sbin"

[PhysSong]

lmms/cmake/linux/package_linux.sh.in

Line 103 in 0059c6e

export PATH="$PATH:/sbin"

I think it should be export PATH="\$PATH:/sbin".

[tresf]

I've committed the patch directly to master. If it causes major issues, we can cherry-pick it to stable-1.2.