STY: update example with preferred plt.subplots()

[mscross]

• Edit first example in streamplot_demo_features.py to conform with preference for fig, ax = plt.subplots(), tweaking style of second example for consistency.
• Add whitespace around / operator for readability (can revert this if preferred).

[tacaswell]

👍 Looks good to me

[WeatherGod]

Strange Travis failure:

======================================================================
FAIL: Github issue #1256 identified a bug in Line.draw method
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.4.2/lib/python3.4/site-packages/nose/case.py", line 198, in runTest
    self.test(*self.arg)
  File "/home/travis/virtualenv/python3.4.2/lib/python3.4/site-packages/matplotlib-1.5.dev1-py3.4-linux-x86_64.egg/matplotlib/testing/decorators.py", line 110, in wrapped_function
    func(*args, **kwargs)
  File "/home/travis/virtualenv/python3.4.2/lib/python3.4/site-packages/matplotlib-1.5.dev1-py3.4-linux-x86_64.egg/matplotlib/tests/test_lines.py", line 58, in test_invisible_Line_rendering
    assert_true(slowdown_factor < slowdown_threshold)
AssertionError: False is not true

I doubt it has anything to do with this change.

[jenshnielsen]

@WeatherGod that one happens once in a while. My understanding is that it tries to measure performance which does somewhat depend on what else is running.