fix travis CI by specifying the node version

SerCeMan · web-flow · commit 0c5d24dbc9a1 · 2021-09-05T15:10:09.000+10:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-  - "node"
+  - 12
 cache: yarn
 
 before_install:
