Merge pull request #578 from FriendsOfSymfony/fix-spellcheck

lock jinja2 version to avoid BC break

Author: dbu

Resources/doc/requirements.txt

@@ -1,7 +1,8 @@
 sphinx==1.8.5
 git+https://github.com/fabpot/sphinx-php.git
-sphinx-rtd-theme
+sphinx-rtd-theme==1.0.0
 sphinxcontrib-spelling
 sphinxcontrib-phpdomain
 pyenchant
 docutils==0.17.1
+jinja2<3.1.0