Remove unreliable dev build

Building from the jruby git repo seems to try to pull artifacts from
other locations, which breaks every so often.

library/jruby

@@ -4,8 +4,6 @@
 1.7.17: git://github.com/cpuguy83/docker-jruby@91121cfab001cb5717097f025b0fcbc5c092a0ce 1.7
 latest: git://github.com/cpuguy83/docker-jruby@91121cfab001cb5717097f025b0fcbc5c092a0ce 1.7
 
-dev: git://github.com/cpuguy83/docker-jruby@9ceb1fcc3eddd71260ff7486f168edbda3974f87 9000
-
 1.7-onbuild: git://github.com/cpuguy83/docker-jruby@91121cfab001cb5717097f025b0fcbc5c092a0ce 1.7/onbuild
 1.7.17-onbuild: git://github.com/cpuguy83/docker-jruby@91121cfab001cb5717097f025b0fcbc5c092a0ce 1.7/onbuild