fixup! Configure CI like the main AVA project

Author: novemberborn

.travis.yml

@@ -1,19 +1,19 @@
 language: node_js
 node_js:
-  - 9
-  - 8
-  - 6
-  - 4
+  - '9'
+  - '8'
+  - '6'
+  - '4'
 env:
   - FRESH_DEPS=false
   - FRESH_DEPS=true
 matrix:
   exclude:
-    - node_js: 9
+    - node_js: '9'
       env: FRESH_DEPS=true
-    - node_js: 6
+    - node_js: '6'
       env: FRESH_DEPS=true
-    - node_js: 4
+    - node_js: '4'
       env: FRESH_DEPS=true
 cache:
   directories: