doc: remove comma in README.md

Grammar edit

PR-URL: nodejs/node#44599
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>

README.md

@@ -1,6 +1,6 @@
 # Node.js
 
-Node.js is an open-source, cross-platform, JavaScript runtime environment.
+Node.js is an open-source, cross-platform JavaScript runtime environment.
 
 For information on using Node.js, see the [Node.js website][].