Update riak_kv to 2.1.5

Author: Brett Hazen

rebar.config

@@ -12,7 +12,7 @@
         {lager, ".*", {git, "git://github.com/basho/lager.git", {tag, "3.2.2"}}},
         {ranch, "0.4.0-p1", {git, "git://github.com/basho/ranch.git", {tag, "0.4.0-p1"}}},
         {ebloom, ".*", {git, "git://github.com/basho/ebloom.git", {tag, "2.0.0"}}},
-        {riak_kv, ".*", {git, "git://github.com/basho/riak_kv.git", {tag, "2.1.4"}}},
+        {riak_kv, ".*", {git, "git://github.com/basho/riak_kv.git", {tag, "2.1.5"}}},
         {riak_repl_pb_api, ".*", {git, "[email protected]:basho/riak_repl_pb_api.git", {tag, "2.4.0"}}}
        ]}.