Test clean install in Travis

.travis.yml

@@ -1,12 +1,18 @@
 sudo: false
 language: ruby
 before_install:
-- gem update --system
+  - gem update --system
-- gem install bundler
+  - gem install bundler
 rvm:
-- 2.1.0
+  - 2.1.0
-script:
+script: bundle exec rake checks
-- bundle exec rake checks
+matrix:
+  include:
+    # Test install on clean system
+    - install: true
+      script:
+        - gem build github_changelog_generator
+        - gem install *.gem
 notifications:
   email:
     recipients: