Fix overly large avatars in emails

Some avatars are insanley huge. This should fix that problem

Fixes CNVS-15478

Test Plan:

- Enable the Show email in notifications account preference
- Setup email servers
- Generate the folloowing notifications
	- Announcement Reply
		- Enable the notification preference
		- Create an Announcement
		- Reply to it
		- Check email
	- Conversation Message
		- Create a Conversation
		- Check email
	- New Discussion Entry
		- Create a discussion
		- Add a comment to it
		- Check email
	- Submission Comment
		- Not really sure??
	- Submission Comment for Teacher
		- Not really sure??

Change-Id: Iacb5059f06be1a4315be69cd9225504cae6267fb
Reviewed-on: https://gerrit.instructure.com/41183
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Horrocks <bhorrocks@instructure.com>
Product-Review: Vincent Gonzalez <vgonzalez@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>