Fix dependencies

.travis.yml

@@ -1,6 +1,12 @@
+sudo: required
+dist: trusty
 language: ruby
 rvm:
   - "1.9.3"
-  - "2.2.4"
+before_install:
+  - sudo apt-get -qq update
+  - sudo apt-get install -y build-essential patch libxslt-dev libxml2-dev
+  - gem install --verbose nokogiri -v 1.6.4
+bundler_args: --without production
 script: bundle exec nanoc