Revert "Test Travis matrix config"

This reverts commit 69125a052f.

.travis.yml

@@ -1,6 +1,4 @@
-matrix:
-  include:
-  - language: ruby
+language: ruby
 rvm:
   - 2.4.1
 
@@ -11,12 +9,3 @@ matrix:
 sudo: false # route your build to the container-based infrastructure for a faster build
 
 cache: bundler # caching bundler gem packages will speed up build
-
-  - language: node_js
-    node_js:
-      - "v12.7.0"
-    branches:
-      only:
-        - master
-    script:
-      - "npm run html-beautify"