pad: Use null as default for userName, userColor options

These options are used as strings, so it doesn't make sense to default
them to a boolean value.

Note that this change has no effect due to a bug in how pad options
are processed; that bug will be fixed in a future commit.

src/node/utils/Settings.js

@@ -165,8 +165,8 @@ exports.padOptions = {
   showChat: true,
   showLineNumbers: true,
   useMonospaceFont: false,
-  userName: false,
-  userColor: false,
+  userName: null,
+  userColor: null,
   rtl: false,
   alwaysShowChat: false,
   chatAndUsers: false,