update travis

Author: SunDi3yansyah

.travis.yml

@@ -1,9 +1,8 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.4.5
-  - 2.5.3
-  - 2.6.0
+  - 2.5.5
+  - 2.6.2
   - ruby-head
 branches:
   only:
@@ -14,11 +13,12 @@ cache:
     - vendor/bundle
     - $HOME/.rvm
 before_install:
-install:
   - travis_retry gem update --system
   - travis_retry gem install bundler
-  - travis_retry bundle
-  - jekyll build
+install:
+  - travis_retry bundle install
+  - travis_retry bundle update
+  - bundle exec jekyll build
 after_success:
 notifications:
   email: false