fix node version

hkollmann · hkollmann · commit e5ebc19d27dd · 2019-10-29T21:08:17.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,6 @@
 language: node_js
-node_js: "node"
+node_js:
+  - 12
 
 before_script:
   - npm install @qooxdoo/compiler 
