Revert "Travis: Temporarily turn off the node.js 12 build"

This reverts commit 82c668e.

.travis.yml

@@ -3,11 +3,11 @@ services:
 language: node_js
 cache:
   directories:
-    - node_modules
+  - node_modules
 node_js:
-  - '8'
-  - '10'
-  - '11'
+  - "8"
+  - "10"
+  - "node"
 
 addons:
   apt:
@@ -17,7 +17,7 @@ addons:
 env: CXX="g++-4.8" CC="gcc-4.8"
 
 before_script:
-  - sudo pip install fonttools brotli zopfli
+    - sudo pip install fonttools brotli zopfli
 
-script: 'npm install && npm run-script travis'
-after_success: '<coverage/lcov.info ./node_modules/coveralls/bin/coveralls.js'
+script: "npm install && npm run-script travis"
+after_success: "<coverage/lcov.info ./node_modules/coveralls/bin/coveralls.js"