fix #451 Change test url in jsonp test

We used to target twitter for testing real jsonp requests. Lately twitter API became rate limited and thus failing from time to time.
This changes to jsfiddle echo service.

(cherry picked from commit 85717e0970a8862a159e9f3492204220c05c0bd9)
fix travis build, upgrading npm version

(cherry picked from commit bc8de6d42b0a489c5990c0ad6142210f1e1658a9)
feat #999 - Added new asserts methods

assertNull, assertNotNull, assertUndefined, assertNotUndefined, assertTruthy, assertFalsy

Close #1004.

(cherry picked from commit d4c6d9907a76614c76f888ecb46ce285b91eed4d)
feat #1137 add tests for util.Dom.getGeometry

(cherry picked from commit 772c77df069c010c006c13fb1b5d540c91970d55)
fix #1137 utils.Dom.getGeometry on absolutely positioned parents

This commit fixes some of the issues in Dom.getGeometry method:

- it adjusted the returned value only on elements with overflow scroll or
  auto, and not when overflow was hidden
- when an element had absolutely positioned ancestors, it was returning
  incorrect values (due to the fact that a parent of absolutely positioned
  element has computed height of 0); particularly it was sometimes wrongly
  returning null while the element was visible in the viewport
- it was sometimes doing calculations unnecessarily

The original issue which triggered the investigation was about SelectBox
inside absolutely positioned parent not displaying the dropdown due to the
call to getGeometry returning null.

Close #1140.

(cherry picked from commit 4bc7708d818b6edc9086056fb98397ec55584e5c)
Update attester version