Destroy lua state before exiting couchscript

couchscript currently exits without destroying the lua
state which means both the lua state and any objects
within it that have not been garbage collected are
technically leaked and caught by valgrind. This change
ensures that the lua state is destroyed before exiting.

Change-Id: I795d439dccb171899463d0d1122865be8ec1f1f0
Reviewed-on: http://review.couchbase.org/61928
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>

src/couchscript.cc

@@ -863,5 +863,6 @@ int main(int argc, char **argv)
     if (top && lua_isnumber(ls, top)) {
         rc = static_cast<int>(lua_tonumber(ls, top));
     }
+    lua_close(ls);
     return rc;
 }