Change apps (ant, maven) to depend on openjdk

Both these apps require some JDK to run, so they have now been changed to depend on `openjdk` Perhaps in the near future `oraclejdk` will appear in the `scoop-extras` bucket which could alternatively be used.

As a side note, should `mvn` be renamed to `maven`? [Maven](http://maven.apache.org/) is what the app is called, but perhaps some people prefer the shorthand `mvn'? Personally I would prefer `maven` and it also makes it easier to find for people using `scoop search`.