Bump minimum Python versions

Followup to #72.

Author: sampsyo

README.rst

@@ -18,7 +18,7 @@ Synopsis
 --------
 
 MediaFile is available `on PyPI`_. Install it by typing ``pip install
-mediafile``. It works on Python 2.7 and Python 3.4 or later. Then:
+mediafile``. It works on Python 3.7 or later. Then:
 
 .. code:: python
 

setup.cfg

@@ -4,7 +4,7 @@ logging-clear-handlers=1
 eval-attr="!=slow"
 
 [flake8]
-min-version=2.7
+min-version=3.7
 # Default pyflakes errors we ignore:
 # - E241: missing whitespace after ',' (used to align visually)
 # - E221: multiple spaces before operator (used to align visually)