Make options argument of child_process.fork optional

According to the docs (and code) this argument is optional.  This also
fixes the warning about non-optional arguments following optional
arguments.

Signed-off-by: Kevin Locke <[email protected]>

Author: kevinoid

child_process.js

@@ -108,7 +108,7 @@ child_process.execFile = function(file, args, options, callback) {};
 /**
  * @param {string} modulePath
  * @param {Array.<string>=} args
- * @param {child_process.Options} options
+ * @param {child_process.Options=} options
  * @return {child_process.ChildProcess}
  */
 child_process.fork = function(modulePath, args, options) {};