diff --git a/.travis.yml b/.travis.yml
index abd393e8..be046949 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,6 @@
 language: node_js
+# To fix the npm version in 4.x
+# refs: https://github.com/travis-ci/travis-ci/issues/4653#issuecomment-194051953
 before_install: 'if [[ `npm -v` != 4* ]]; then npm i -g npm@4; fi'
 matrix:
   include: