fix ci config (#76)

Author: gucong3000

circle.yml

@@ -1,6 +1,12 @@
 machine:
   node:
-    version: 6
+    version: stable
+
+dependencies:
+  pre:
+    - sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" > /etc/apt/sources.list.d/google-chrome.list'
+    - sudo apt-get update
+    - sudo apt-get install google-chrome-stable
 
 test:
   override: