Msftidy: Fix explicit rubygems

[todb-r7]

This knocks out the last non-datastore (and now non-comma) msftidy complaint.

Verification

• When running msftidy, you should not see any results. For example, after fix, you should see:

$ tools/msftidy.rb modules/ | grep -v -e datastore -e comma
$

and not:

$ tools/msftidy.rb modules/ | grep -v -e datastore -e comma
modules/auxiliary/crawler/msfcrawler.rb - [WARNING] Explicitly requiring/loading rubygems is not necessary