doc: remove comma in README.md

Grammar edit

Author: Taha-Chaudhry

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][].