core: update ChangeLog (issue #1920)

ChangeLog.adoc

@@ -20,6 +20,7 @@ New features::
   * core: add key kbd:[Alt+K] (upper case) to grab raw key and its command (issue #1238)
   * core: add option `key` in command `/debug` (issue #1238)
   * core: force ctrl keys to lower case when they are added (issue #1875)
+  * core: use 256 colors by default and always allow 256 colors, find nearest color if less colors are available in terminal (issue #1920)
   * core: insert multiple pasted lines in input instead of sending immediately, add keys to move and delete in a single line and whole input, add option weechat.look.input_multiline_lead_linebreak (issue #1502, issue #1503, issue #1504)
   * core: render newline characters in chat line messages (issue #1908)
   * core: don't split on newline characters in printf_date_tags when input_multiline is set (issue #1909)