Make it more clear that these are OpenJDK versions, leaving room for future flavors (Oracle, IBM, Zing, etc)

Fixes #8
```console
$ ./generate-stackbrew-library.sh
# maintainer: InfoSiftr <github@infosiftr.com> (@infosiftr)

openjdk-6b32-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
openjdk-6b32: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
openjdk-6-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
openjdk-6: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
6b32-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
6b32: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
6-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk
6: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-6-jdk

openjdk-7u65-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
openjdk-7u65: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
openjdk-7-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
openjdk-7: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
7u65-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
7u65: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
7-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
7: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk
latest: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-7-jdk

openjdk-8u40-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
openjdk-8u40: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
openjdk-8-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
openjdk-8: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
8u40-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
8u40: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
8-jdk: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
8: git://github.com/docker-library/docker-java@5632fcebd38b14465013f236be8fcd0f5bfdc234 openjdk-8-jdk
```

This also leaves room explicitly for `-jre` variants (ie, #7).