upgrade tinymce from 4.0.1 to 4.0.20
Explicitly cast value of fetched zIndex to string, because in IE11 this value is an int,
and the test compares it to a string
Merge pull request #360 from plone/pysailor-tinymce-4-0-20

Upgrade tinymce from 4.0.1 to 4.0.20