tools: fix typo in .eslintrc.js

Refs: https://github.com/nodejs/node/pull/18566

PR-URL: https://github.com/nodejs/node/pull/21449
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

.eslintrc.js

@@ -131,7 +131,7 @@ module.exports = {
       {
         object: 'assert',
         property: 'equal',
-        message: 'Use assert.astrictEqual() rather than assert.equal().',
+        message: 'Use assert.strictEqual() rather than assert.equal().',
       },
       {
         object: 'assert',