STY: Flake8

Upgrade the version of the flake8, pep8, and mccabe PyPI packages, and
make the code changes necessary for compatibility with the updated
packages.

tests/test_examples.py

@@ -19,7 +19,6 @@
 # Disable plotting
 #
 import matplotlib
-matplotlib.use('Agg')
 
 import os
 from os import path
@@ -33,6 +32,8 @@ except ImportError:
 import fnmatch
 import imp
 
+matplotlib.use('Agg')
+
 
 def test_examples():
     os.chdir(example_dir())