include date of last release

Author: joshgoebel

README.md

@@ -14,6 +14,8 @@
 Version 9 has reached end-of-support and will receive no future updates.
 It may include unpatched security vulnerabiites.  Please upgrade to version 10.
 
+*The last release was 9.18.4 on November 18, 2020.*
+
 Please see [VERSION_10_UPGRADE.md](https://github.com/highlightjs/highlight.js/blob/master/VERSION_10_UPGRADE.md) and perhaps [SECURITY.md](https://github.com/highlightjs/highlight.js/blob/master/SECURITY.md).
 
 ---

tools/build.js

@@ -64,7 +64,6 @@ let commander = require('commander');
 let path      = require('path');
 let Queue     = require('gear').Queue;
 let registry  = require('./tasks');
-let fs = require('fs');
 
 let build, dir = {};