ci: add node-14.x to workflow (#276)

diff --git a/.travis.yml b/.travis.yml
index 1df847e..7495398 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,6 +4,7 @@
 node_js:
     - 10
     - 12
+    - 14
 
 install:
     - npm install