Add libwebp-dev to ubuntu-precise; resolves travis-ci/apt-package-whitelist#1255
Add libwebp-dev to ubuntu-precise; resolves travis-ci/apt-package-whitelist#1255

Packages: libwebp-dev libwebp5 libwebpmux1 libwebpdemux1 webp

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