fixed loading of tinymce and its plugins

test plan:

- tinymce specs should pass
- tinymce and its plugins should behave normally

Change-Id: Iced4ce068b0ee51781b23e8285a1e277d83bb44a
Reviewed-on: https://gerrit.instructure.com/29854
Reviewed-by: Stanley Stuart <stanley@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>