Prevent scroll reset on keypress

No need to replace content with content on each keypress, it resets scroller position in case of overflow.

Enyo-DCO-1.1-Signed-Off-By: Rafa Bernad (rafa.bernad@newn.es)
Update RichText.js

Update with proposed approach.
Merge pull request #306 from Newness/patch-1

Prevent scroll reset on keypress

Reviewed-By: Ben Combee (ben.combee@lge.com)