ci: Test in Node.js 10 and 11, deploy with Node.js 10 (#3069)

.travis.yml

@@ -1,13 +1,13 @@
 language: node_js
 node_js:
-  - 8
-  - 9
+  - 10
+  - 11
 install: npm install
 script: bash ./travis/test.sh
 jobs:
   include:
     - stage: deploy
-      node_js: 9
+      node_js: 10
       script: bash ./travis/deploy.sh
       env:
         - ENCRYPTION_LABEL="af862fa96d3e"