docs: fix typos in JSDoc comments

closes #5117

Author: raksbisht

examples/markdown/index.js

@@ -26,7 +26,7 @@ app.engine('md', function(path, options, fn){
 
 app.set('views', path.join(__dirname, 'views'));
 
-// make it the default so we dont need .md
+// make it the default, so we don't need .md
 app.set('view engine', 'md');
 
 app.get('/', function(req, res){

lib/router/index.js

@@ -36,7 +36,7 @@ var toString = Object.prototype.toString;
  * Initialize a new `Router` with the given `options`.
  *
  * @param {Object} [options]
- * @return {Router} which is an callable function
+ * @return {Router} which is a callable function
  * @public
  */