chore (ci): remove deprecated sudo: false in .travis.yml

https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration

Author: DirtyF

.travis.yml

@@ -1,19 +1,22 @@
 language: ruby
+cache:bundler
+rvm:
+  - 2.6
+  - 2.4
+
 script : script/cibuild
-sudo: false
-notifications:
-  email: false
+
 branches:
   only:
     - master
-rvm:
-  - 2.6
-  - 2.4
 env:
-  - ""
   - JEKYLL_VERSION=3.7.4
+
 matrix:
   include:
     - # GitHub Pages
-      rvm: 2.5.1
+      rvm: 2.5.3
       env: GH_PAGES=true
+
+notifications:
+  email: false