Add libgflags-dev to ubuntu-precise; resolves travis-ci/apt-package-whitelist#1312
Add libgflags-dev to ubuntu-precise; resolves travis-ci/apt-package-whitelist#1312

Packages: libgflags-dev libgflags2v5 libgflags-doc

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