Snap author in "was shared with you" emails

[Robert Gildein]

I recently received an email about a snap shared with me,
the email claiming that it was shared by the author. However,
this snap was shared by another collaborator and at the
same time the author's email no longer exists.

So I think this email should include the name and email
address of the collaborator who shared the snap with me.

What I got:
```
The package <name> (<name>) has been shared with you by
<author name> <author email>. To accept this share, please visit:
```
What I expected:
```
The package <name> (<name>) has been shared with you by
<collaborator name> <collaborator email>. To accept this share, please visit:

```
Thanks