.travis.yml: add another ignore

.travis.yml

@@ -5,7 +5,7 @@ script:
   - 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”.'
+  - ~/.local/bin/html5validator --root _site/ --ignore 'Bad value “Content-Security-Policy” for attribute “http-equiv” on element “meta”.' '“&” did not start a character reference. (“&” probably should have been escaped as “&”.)'
 rvm: 2.1
 notifications:
     email: false