.travis.yml in rmagick-3.1.0 vs .travis.yml in rmagick-3.2.0

- old
+ new
@@ -1,40 +1,58 @@
 language: ruby
 
 cache:
   directories:
-    - ~/.ccache
+    - ~/.cache/rubocop_cache
     - vendor/bundle
     - build-ImageMagick
 
+dist: xenial
+addons:
+  apt:
+    packages:
+      - build-essential
+      - libx11-dev
+      - libxext-dev
+      - zlib1g-dev
+      - liblcms2-dev
+      - libpng-dev
+      - libjpeg-dev
+      - libfreetype6-dev
+      - libxml2-dev
+      - libtiff5-dev
+      - libwebp-dev
+      - ghostscript
+      - ccache
+
 os:
   - linux
 
 sudo: required
 
 env:
   - IMAGEMAGICK_VERSION=6.7.7-10
   - IMAGEMAGICK_VERSION=6.7.7-10 CONFIGURE_OPTIONS=--enable-hdri
   - IMAGEMAGICK_VERSION=6.8.9-10
   - IMAGEMAGICK_VERSION=6.8.9-10 CONFIGURE_OPTIONS=--enable-hdri
-  - IMAGEMAGICK_VERSION=6.9.10-40
-  - IMAGEMAGICK_VERSION=6.9.10-40 CONFIGURE_OPTIONS=--enable-hdri
+  - IMAGEMAGICK_VERSION=6.9.10-49
+  - IMAGEMAGICK_VERSION=6.9.10-49 CONFIGURE_OPTIONS=--enable-hdri
 
 before_install:
-  - source before_install_$TRAVIS_OS_NAME.sh
+  - /bin/bash before_install_$TRAVIS_OS_NAME.sh
 
 install: bundle install --path=vendor/bundle --verbose
 
 rvm:
-  - 2.3
-  - 2.4
-  - 2.5
+  - 2.3.8
+  - 2.4.5
+  - 2.5.3
   - 2.6
 
 matrix:
   include:
     - rvm: 2.3
-      env: STYLE_CHECKS=true IMAGEMAGICK_VERSION=6.8.9-10
+      env: STYLE_CHECKS=true
 
 notifications:
   webhooks:
     urls:
       - https://webhooks.gitter.im/e/a98c1112f5d60f97a532