Fix test_novice.test_update_on_save failure on Windows

On Windows, tempfile.NamedTemporaryFile() can not be opened a second time. See <http://docs.python.org/2/library/tempfile.html#tempfile.NamedTemporaryFile>

```
======================================================================
ERROR: test_novice.test_update_on_save
----------------------------------------------------------------------
Traceback (most recent call last):
  File "X:\Python34\lib\site-packages\nose\case.py", line 198, in runTest
    self.test(*self.arg)
  File "X:\Python34\lib\site-packages\skimage\novice\tests\test_novice.py", line 115, in test_update_on_save
    pic.save(tmp.name)
  File "X:\Python34\lib\site-packages\skimage\novice\_novice.py", line 267, in save
    io.imsave(path, self._rescale(self.array))
  File "X:\Python34\lib\site-packages\skimage\io\_io.py", line 155, in imsave
    return call_plugin('imsave', fname, arr, plugin=plugin, **plugin_args)
  File "X:\Python34\lib\site-packages\skimage\io\manage_plugins.py", line 209, in call_plugin
    return func(*args, **kwargs)
  File "X:\Python34\lib\site-packages\skimage\io\_plugins\pil_plugin.py", line 119, in imsave
    img.save(fname, format=format_str)
  File "X:\Python34\lib\site-packages\PIL\Image.py", line 1459, in save
    fp = builtins.open(fp, "wb")
PermissionError: [Errno 13] Permission denied: 'C:\\Users\\gohlke\\AppData\\Local\\Temp\\tmpyvdigal3.jpg'
```