Update README.md

changed misspelled word
Merge pull request #2428 from luislobo/patch-1

Update lib/app/README.md
Ractive renderHTML is deprecated

starting with Ractive 0.3.8
> `ractive.toHTML()` replaces `ractive.renderHTML()`
Merge pull request #2429 from sleewoo/master

Ractive renderHTML is deprecated
Merge branch 'master' of https://github.com/balderdashy/sails into sails

* 'master' of https://github.com/balderdashy/sails:
  Ractive renderHTML is deprecated
  Update README.md