use spec_helper instead of just ams_spec_helper

Using just ams_spec_helper seems to cause issues on
CI due to dependening on some libraries that have been
extracted from Canvas.

Change-Id: If64c7281b1e9cf0ca18c6c671f180e2010fa4bf7
Reviewed-on: https://gerrit.instructure.com/29460
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>