child_process: fix order of args to errnoException()

lib/child_process.js

@@ -440,7 +440,7 @@ ChildProcess.prototype.spawn = function(options) {
 
     this._internal.close();
     this._internal = null;
-    throw errnoException('spawn', errno);
+    throw errnoException(errno, 'spawn');
   }
 
   this.pid = this._internal.pid;