fix spawn call, customFds ain't supported yet

lib/_debugger.js

@@ -1286,7 +1286,7 @@ Interface.prototype.trySpawn = function(cb) {
 
   this.killChild();
 
-  this.child = spawn(process.execPath, args, { customFds: [0, 1, 2] });
+  this.child = spawn(process.execPath, args);
 
   this.child.stdout.on('data', this.childPrint.bind(this));
   this.child.stderr.on('data', this.childPrint.bind(this));