Sphinx's needs_sphinx setting value needs an update

[Ramiro Morales]

Right now it's '1.3' and using Spinx 1.3.6 (last 1.3.x release) fails under Python 3:

$ make clean html
rm -rf _build/*
sphinx-build -b djangohtml -n -d _build/doctrees -D language=en   . _build/html
Running Sphinx v1.3.6
making output directory...
A Translator for the djangohtml builder is changed.
A Translator for the json builder is changed.
loading translations [en]... done
loading pickled environment... not yet created
loading intersphinx inventory from http://sphinx-doc.org/objects.inv...
loading intersphinx inventory from http://initd.org/psycopg/docs/objects.inv...
loading intersphinx inventory from https://docs.python.org/3/objects.inv...
building [mo]: targets for 0 po files that are out of date
building [djangohtml]: targets for 395 source files that are out of date
updating environment: 395 added, 0 changed, 0 removed
reading sources... [100%] topics/testing/tools                                                                                                                                              
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [ 11%] internals/contributing/triaging-tickets                                                                                                                            
Exception occurred:
  File "/home/user/.virtualenvs/djt35/lib/python3.5/site-packages/docutils/writers/_html_base.py", line 736, in depart_document
    assert not self.context, 'len(context) = %s' % len(self.context)
AssertionError: len(context) = 1
The full traceback has been saved in /tmp/sphinx-err-el3e46h0.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
make: *** [html] Error 1

Same error happens with 1.4.x.

There are some regressions in Sphinx 1.5.x which make 1.5.5 the first release in which Django docs building is stable.

Sphinx supports specifying micro version componente in this settings since version 1.4.

[Ramiro Morales <cramm0@…>]

In e67733a:

Fixed #28963 -- Raised minimum Sphinx version.