fix validation errors in .travis.yml

* remove obsolete `sudo` key
* add `os: linux` default
* make the cache directories arrays as requested by the schema
* `matrix` -> `jobs`
* some YAML reformatting

Author: DavidS

.travis.yml

@@ -1,4 +1,4 @@
-sudo: false
+os: linux
 language: ruby
 bundler_args: "--without development"
 script:
@@ -10,8 +10,8 @@ script:
 cache: bundler
 branches:
   except:
-  - release-prep
-matrix:
+    - release-prep
+jobs:
   include:
     - rvm: 2.4.3
       env: PUPPET_GEM_VERSION='~> 5' SIMPLECOV=yes # 5.5
@@ -20,15 +20,15 @@ matrix:
       before_cache: pushd ~/.rvm && rm -rf archives rubies/ruby-2.2.7 rubies/ruby-2.3.4 && popd
       cache:
         bundler: true
-        directories: ~/.rvm
+        directories: [~/.rvm]
       before_install: rvm use jruby-1.7.26 --install --binary --fuzzy && gem install bundler -v '~> 1.7.0'
     # disable coverage on jruby9k as this confuses codecov
     - env: RVM="jruby-9.1.9.0" PUPPET_GEM_VERSION='~> 5' JRUBY_OPTS="--debug"
       dist: trusty
       before_cache: pushd ~/.rvm && rm -rf archives rubies/ruby-2.2.7 rubies/ruby-2.3.4 && popd
       cache:
         bundler: false
-        directories: ~/.rvm
+        directories: [~/.rvm]
       before_install: rvm use jruby-9.1.9.0 --install --binary --fuzzy
     - rvm: 2.5.1
       env: CHECK=rubocop