feat: set up drill to be completed by _known_hosts

Included with the ldns library, the drill tool is similar to dig and is
used for DNS lookups. As such, it greatly benefits from host completion.

Author: foutrelis

bash_completion

@@ -2186,7 +2186,7 @@ _known_hosts_real()
 
 } # _known_hosts_real()
 complete -F _known_hosts traceroute traceroute6 \
-    fping fping6 telnet rsh rlogin ftp dig mtr ssh-installkeys showmount
+    fping fping6 telnet rsh rlogin ftp dig drill mtr ssh-installkeys showmount
 
 # This meta-cd function observes the CDPATH variable, so that cd additionally
 # completes on directories under those specified in CDPATH.