Revert "Test Travis matrix config"

This reverts commit 69125a052f.

.travis.yml

@@ -1,22 +1,11 @@
-matrix:
-  include:
-  - language: ruby
-    rvm:
-      - 2.4.1
+language: ruby
+rvm:
+  - 2.4.1
 
-    # Assume bundler is being used, therefore
-    # the `install` step will run `bundle install` by default.
-    script: ./build.sh
+# Assume bundler is being used, therefore
+# the `install` step will run `bundle install` by default.
+script: ./build.sh
 
-    sudo: false # route your build to the container-based infrastructure for a faster build
+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"
+cache: bundler # caching bundler gem packages will speed up build