doc pages offcanvas toggle anchor requires href

 Updated offcanvas examples to include href attribute on toggle anchors.

 The offcanvas toggle anchors require an href attribute to work properly
 on iphones as discussed here
 http://foundation.zurb.com/forum/posts/1651-cant-get-off-canvas-to-toggle-on-mobile
Merge pull request #5227 from here/doc-offcanvas-anchor-href

doc pages offcanvas toggle anchor requires href