Add Node.js 12 to CI Services (#53)

diff --git a/.travis.yml b/.travis.yml
index c23ef3c..5163e1f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -27,6 +27,7 @@
   - 6
   - 8
   - 10
+  - 12
 
 install:
   - npm install