Fix #812: Write a trailing newline character to the Mix lockfile.

Author: alexrp

lib/mix/lib/mix/deps/lock.ex

@@ -33,7 +33,7 @@ defmodule Mix.Deps.Lock do
         %b("#{app}": #{inspect rev, raw: true})
       end
 
-      File.write! lockfile, "[ " <> lines <> " ]"
+      File.write! lockfile, "[ " <> lines <> " ]\n"
     end
   end