chore: better formatting of travis file

Author: TheAlexLichter

.travis.yml

@@ -1,14 +1,14 @@
 language: node_js
 node_js:
-- "10"
-- "11"
+  - "10"
+  - "11"
 cache:
   yarn: true
   directories:
-  - node_modules
+    - node_modules
 install:
-- yarn
+  - yarn
 script:
-- yarn test
+  - yarn test
 after_success:
-- yarn coverage
+  - yarn coverage