Bug#696451: Should depend on java2-runtime-headless rather than java2-runtime

[rufo]

Package: clojure1.4
Version: 1.4.0+dfsg-2

Clojure does not require the full versions of JREs.  It works fine with 
headless versions, which have fewer dependencies and do not needlessly 
pull in x11-related packages.

I believe the current dependency of this package on java2-runtime should 
be changed to java2-runtime-headless to reflect this.