Use std::make_unique instead of ::make_unique
Use std::make_unique instead of ::make_unique

When the backport of C++14 make_unique() was added to platform, it
incorrectly was added to the global namespace instead of std. This
means it isn't a drop-in replacement - it /should/ be in the std
namespace.

Change-Id: I079175bf8e3938f1aa462b09c75a34e206b523de
Reviewed-on: http://review.couchbase.org/71040
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

membase/ep-engine,daverigby/ep-engine,couchbase/ep-engine,couchbase/ep-engine,membase/ep-engine,daverigby/kv_engine,membase/ep-engine,daverigby/kv_engine,daverigby/ep-engine,couchbase/ep-engine,daverigby/kv_engine,couchbase/ep-engine,daverigby/ep-engine,daverigby/ep-engine,membase/ep-engine,daverigby/kv_engine