fix csp warning about unsafe-inline style-src

Showing and hiding an off-canvas menu with content-security-policy enabled (via ember-cli) results in the following~

    [Report Only] Refused to apply inline style because it violates the following Content Security Policy directive~

Changing the way that OffCanvas.hide() restors the style addresses this warning. e.g., `$(this).attr('style', ...)`~

For more information about content-security-policy, see http://content-security-policy.com/.

js/offcanvas.js

@@ -236,7 +236,8 @@
       
       elements.removeClass('canvas-sliding')
       elements.add(this.$element).add('body').each(function() {
-        $(this).attr('style', $(this).data('offcanvas-style')).removeData('offcanvas-style')
+        $(this).style = $(this).data('offcanvas-style')
+        $(this).removeData('offcanvas-style')
       })
 
       this.$element.trigger('hidden.bs.offcanvas')