Add clojure alpine-onbuild image

Got this merged into the official repo, so time to add it in here.

library/clojure

@@ -4,7 +4,9 @@
 latest: git://github.com/Quantisan/docker-clojure@0d4a0abe13497a6081ebd080e83d1be0abab3f59
 onbuild: git://github.com/Quantisan/docker-clojure@0d4a0abe13497a6081ebd080e83d1be0abab3f59 onbuild
 alpine: git://github.com/Quantisan/docker-clojure@534102a7ee7e6f4825e86a648a52c44cc25eb39d alpine
+alpine-onbuild: git://github.com/Quantisan/docker-clojure@73e7427a6cfec285a3d901e4a9ae25b8109c3d0c alpine-onbuild
 
 lein-2.6.1: git://github.com/Quantisan/docker-clojure@0d4a0abe13497a6081ebd080e83d1be0abab3f59
 lein-2.6.1-onbuild: git://github.com/Quantisan/docker-clojure@0d4a0abe13497a6081ebd080e83d1be0abab3f59 onbuild
 lein-2.6.1-alpine: git://github.com/Quantisan/docker-clojure@534102a7ee7e6f4825e86a648a52c44cc25eb39d alpine
+lein-2.6.1-alpine-onbuild: git://github.com/Quantisan/docker-clojure@73e7427a6cfec285a3d901e4a9ae25b8109c3d0c alpine-onbuild