code: add is_pkg flag

Author: jcs090218

src/env.js

@@ -19,4 +19,7 @@
 
 "use strict";
 
+const path = require('path');
+
 global.UTIL = require('./util');
+global.IS_PKG = !path.basename(process.execPath).startsWith('node');

src/util.js

@@ -31,7 +31,10 @@ function _remove_undefined(arr) {
 }
 
 /* Return plugin directory */
-function plugin_dir() { return path.join(__dirname, '..'); }
+function plugin_dir() {
+  let root = (IS_PKG) ? process.execPath : __dirname;
+  return path.join(root, '..');
+}
 
 /**
  * Define flag with proper alias flag.