fs: use arrow function for lexical this

Extra scrutiny required for this change

Refs nodejs#7414

lib/fs.js

@@ -1786,7 +1786,16 @@ ReadStream.prototype.destroy = function() {
 
 
 ReadStream.prototype.close = function(cb) {
-  var self = this;
+  const close = (fd) => {
+    fs.close(fd || this.fd, (er) => {
+      if (er)
+        this.emit('error', er);
+      else
+        this.emit('close');
+    });
+    this.fd = null;
+  };
+
   if (cb)
     this.once('close', cb);
   if (this.closed || typeof this.fd !== 'number') {
@@ -1798,16 +1807,6 @@ ReadStream.prototype.close = function(cb) {
   }
   this.closed = true;
   close();
-
-  function close(fd) {
-    fs.close(fd || self.fd, function(er) {
-      if (er)
-        self.emit('error', er);
-      else
-        self.emit('close');
-    });
-    self.fd = null;
-  }
 };