.travis.yml: fix validation

ignore the Upgrade Insecure Requests error

.travis.yml

@@ -1,11 +1,11 @@
 language: ruby
 sudo: false
 script:
-  - "gem install github-pages"
-  - "jekyll build --drafts"
-    "python2 --version && python2 -m pip --version"
-  - "python2 -m pip install html5validator --user --upgrade"
-  - "~/.local/bin/html5validator --root _site/|true"
+  - gem install github-pages
+  - jekyll build --drafts
+  - python2 --version && python2 -m pip --version
+  - python2 -m pip install html5validator --user --upgrade
+  - ~/.local/bin/html5validator --root _site/ --ignore 'Bad value “Content-Security-Policy” for attribute “http-equiv” on element “meta”.'
 rvm: 2.1
 notifications:
     email: false