python3 issue

> python setup.py showdocs

> running showdocs
> reST to HTML conversion available at at http://localhost:6969/ - press CTRL+C to interrupt
> 127.0.0.1 - - [04/Apr/2017 10:17:37] "GET /0.551963301487 HTTP/1.1" 200 -
> ----------------------------------------
> Exception happened during processing of request from ('127.0.0.1', 58713)
> Traceback (most recent call last):
> File "/usr/local/Cellar/python/2.7.12_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 290, in _handle_request_noblock
> self.process_request(request, client_address)
> File "/usr/local/Cellar/python/2.7.12_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 318, in process_request
> self.finish_request(request, client_address)
> File "/usr/local/Cellar/python/2.7.12_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 331, in finish_request
> self.RequestHandlerClass(request, client_address, self)
> File "/usr/local/Cellar/python/2.7.12_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 652, in __init__
> self.handle()
> File "/usr/local/Cellar/python/2.7.12_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/BaseHTTPServer.py", line 340, in handle
> self.handle_one_request()
> File "/usr/local/Cellar/python/2.7.12_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/BaseHTTPServer.py", line 328, in handle_one_request
> method()
> File "/Users/sobolev/.virtualenvs/django_split_settings/lib/python2.7/site-packages/collective/checkdocs/__init__.py", line 41, in do_GET
> print(self.value.encode('utf-8'), file=f)
> TypeError: unicode argument expected, got 'str'

I can send a PR with the fix, if it's fine.