Add dependency on underscore
Remove last example in parsing/is-valid

The moment#isValid method still works.
Merge branch 'gh-pages' of github.com:liunian/momentjs.com into liunian-gh-pages

# By liunian
# Via liunian
* 'gh-pages' of github.com:liunian/momentjs.com:
  Remove last example in parsing/is-valid
  Add dependency on underscore
Merge branch 'liunian-gh-pages' into gh-pages

* liunian-gh-pages:
  Remove last example in parsing/is-valid
  Add dependency on underscore