Update .travis.osx.yml

- remove gmp & mpfr from the precompiled package because it sometimes causes a build failure for mpfr.
- take out -v option when extracting gcc.tar.bz2
[skip ci]
Add implicit argument management to lean frontend.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add implicit argument declarations to lean parser.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>