Add libmpfr4 to ubuntu-trusty; resolves travis-ci/apt-package-whitelist#3800
Add libmpfr4 to ubuntu-trusty; resolves travis-ci/apt-package-whitelist#3800

Packages: libmpfr4 libmpfr4-dbg libmpfr-dev libmpfr-doc

travis-ci/apt-package-whitelist,travis-ci/apt-package-whitelist