Minor fix to required_if rule

Tweaked signature to state it accepts multiple values.
Use Vagrant IP address for domain linking
Better SSH key comment

SSH key comments are not usually emails, they are only emails if they are used for a website where identification is done using email and not using a username. So for example, a website like Github where every user pushes as git@ is something where an email would make sense.

Usually the comments on SSH keys are user@hostname, since the homestead box has no particular hostname other than localhost @homestead is a good replacement here. The naming is more conventional this way and teaches practice right away that you should use different keys for different hosts.

Minor detail. Not like comments matter for anything at all.
Added a noun and added a serial (AKA Oxford) comma

Nitpicky, but every little thing counts.
Merge pull request #937 from jkingsman/4.2

Added a noun and added a serial (AKA Oxford) comma
Merge pull request #934 from paulofreitas/patch-2

Minor fix to required_if rule
Merge pull request #936 from aFreshMelon/patch-1

Better SSH key comment
Merge pull request #935 from driesvints/patch-1

Use Vagrant IP address for domain linking
Merge branch '4.2'