Cloud not make JRuby build pass on Xenial, reverting back to Trusty

https://travis-ci.org/carrierwaveuploader/carrierwave/builds/583003552

When we try Xenial next time, we need following sinppet in before_script:
- sudo sed -ie 's/rights="none" pattern="PDF"/rights="read|write" pattern="PDF"/' /etc/ImageMagick-6/policy.xml

Author: mshibuya

.travis.yml

@@ -1,11 +1,13 @@
+dist: trusty
+
 language: ruby
 
 cache: bundler
 
 rvm:
   - 2.5.5
   - 2.6.2
-  - jruby-9.2.6.0
+  - jruby-9.2.8.0
 
 gemfile:
   - gemfiles/rails-5-2.gemfile
@@ -18,7 +20,6 @@ before_install:
 
 before_script:
   - psql -c 'create database carrierwave_test;' -U postgres
-  - sudo sh -c 'echo '\''<policymap><policy domain="coder" rights="read|write" pattern="PDF" /></policymap>'\'' > /etc/ImageMagick-6/policy.xml'
 
 matrix:
   include:
@@ -39,7 +40,7 @@ matrix:
     - rvm: jruby-head
       gemfile: gemfiles/rails-5-2.gemfile
   exclude:
-    - rvm: jruby-9.2.6.0
+    - rvm: jruby-9.2.8.0
       gemfile: gemfiles/rails-6-0.gemfile
   allow_failures:
     - rvm: ruby-head