Avoid modifying strings.
Avoid modifying strings.

Opal doesn't support modification of strings, so convert this code to
use += instead of <<.

Signed-off-by: brian m. carlson <738bdd359be778fee9f0fc4e2934ad72f436ceda@crustytoothpaste.net>

bk2204/daniel-ruby,bk2204/daniel-ruby