Fix __expand_tilde_by_ref usage example.

bash_completion

@@ -604,7 +604,7 @@ _available_interfaces()
 # a dollar sign variable ($) or asterisk (*) is not expanded.
 # Example usage:
 #
-#    $ v="~"; __expand_tilde v; echo "$v"
+#    $ v="~"; __expand_tilde_by_ref v; echo "$v"
 #
 # Example output:
 #