use newer versions of NodeJS

Author: rvalitov

.travis.yml

@@ -3,13 +3,14 @@ sudo: false
 language: node_js
 
 node_js:
-  - "4"
-  - "5"
-  - "6"
+  - "10"
+  - "12"
+  - "13"
+  - "stable"
 
 matrix:
   fast_finish: true
 
 cache:
   directories:
-    - node_modules
+    - node_modules