Update ghost image

* Clean up build artifacts (docker-library/ghost#4)

library/ghost

@@ -1,6 +1,6 @@
 # maintainer: InfoSiftr <[email protected]> (@infosiftr)
 
-0.5.10: git://github.com/docker-library/ghost@2b93aa26432d878a6d3b40d8cdc918a103ed2661
-0.5: git://github.com/docker-library/ghost@2b93aa26432d878a6d3b40d8cdc918a103ed2661
-0: git://github.com/docker-library/ghost@2b93aa26432d878a6d3b40d8cdc918a103ed2661
-latest: git://github.com/docker-library/ghost@2b93aa26432d878a6d3b40d8cdc918a103ed2661
+0.5.10: git://github.com/docker-library/ghost@a908596689f8244d312b6ad5975e04c9eede5ce9
+0.5: git://github.com/docker-library/ghost@a908596689f8244d312b6ad5975e04c9eede5ce9
+0: git://github.com/docker-library/ghost@a908596689f8244d312b6ad5975e04c9eede5ce9
+latest: git://github.com/docker-library/ghost@a908596689f8244d312b6ad5975e04c9eede5ce9