Add 379 RPL_WHOISMODES to codes

Fixes #47.

Per https://www.alien.net.au/irc/irc2numerics.html, it has a conflicting
definition with aircd, but aircd (as noted previously) doesn't seem to
be in major use.

Author: Throne3d

lib/codes.js

@@ -311,6 +311,10 @@ module.exports = {
         name: 'rpl_whoishost',
         type: 'reply'
     },
+    379: {
+        name: 'rpl_whoismodes',
+        type: 'reply'
+    },
     381: {
         name: 'rpl_youreoper',
         type: 'reply'