jdk 1.8.0-25: New formula for Linuxbrew

This formula doesn't work out-of-the-box because Oracle requires accepting click-through license, which doesn't work with curl. You can instead download the file and save it as
`~/.cache/Homebrew/jdk-1.8.0-25.tar.gz`, then run
`brew install https://raw.githubusercontent.com/Homebrew/linuxbrew/jdk/Library/Formula/jdk.rb`.