travis: use built-in mono support
travis: use built-in mono support

We're about to require nuget, and it's just a lot easier to just
use the built-in mono support than cobbling together a bunch of
separate tools into a working toolset.

This also matches what Fuse Studio does.

cbaggers/fuselibs-public,kusma/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,cbaggers/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,cbaggers/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,cbaggers/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,cbaggers/fuselibs-public,kusma/fuselibs-public,nekronos/fuselibs-public,nekronos/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,cbaggers/fuselibs-public,fusetools/fuselibs-public,nekronos/fuselibs-public,cbaggers/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,nekronos/fuselibs-public