fix build failure with Python 3.6

[tverbeke]

Without the change, there is a decoding error:

Traceback (most recent call last):
  File "setup.py", line 32, in <module>
    long_description=readme(),
  File "setup.py", line 27, in readme
    return f.read()
  File "/usr/lib/python3.6/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 637: ordinal not in range(128)

with the change, build and installation works fine.

To reproduce the problem, try installing it using this Dockerfile:

FROM ubuntu:18.04
RUN apt-get update && apt-get install -y locales python3-pip

RUN echo "en_US.UTF-8 UTF-8" >> /etc/locale.gen \
  && locale-gen en_US.utf8 \
  && /usr/sbin/update-locale LANG=en_US.UTF-8

RUN pip3 install --upgrade mkdocs
RUN pip3 install pygments
RUN pip3 install pymdown-extensions
RUN pip3 install python-markdown-math

# this step fails
RUN pip3 install fontawesome_markdown

[bmcorser]

Cool, thanks. Why not add a test including your image definition. Feel free to assume the developer has Docker installed :)

[Mte90]

I can confirm this issue, very annoying.