Fix: Use self.getConfig to access a specific config value.
Fix: Use self.getConfig to access a specific config value.

This fix allows this extension to work with python-markdown v2.4, which is what ships with Ubuntu 14 LTS. Without this fix, I see:

C:\blah>python -m markdown -x enki.plugins.preview.mdx_math
Traceback (most recent call last):
  File "C:\Python27\lib\runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "C:\Python27\lib\runpy.py", line 72, in _run_code
    exec code in run_globals
  File "C:\Python27\lib\site-packages\markdown\__main__.py", line 87, in <module>
    run()
  File "C:\Python27\lib\site-packages\markdown\__main__.py", line 81, in run
    markdown.markdownFromFile(**options)
  File "C:\Python27\lib\site-packages\markdown\__init__.py", line 438, in markdownFromFile
    md = Markdown(**kwargs)
  File "C:\Python27\lib\site-packages\markdown\__init__.py", line 137, in __init__
    configs=kwargs.get('extension_configs', {}))
  File "C:\Python27\lib\site-packages\markdown\__init__.py", line 165, in registerExtensions
    ext.extendMarkdown(self, globals())
  File "C:\Users\bjones\Documents\python-markdown-math\mdx_math.py", line 38, in extendMarkdown
  File "C:\Python27\lib\site-packages\markdown\extensions\__init__.py", line 28, in getConfigs
    return dict([(key, self.getConfig(key)) for key in self.config.keys()])
AttributeError: 'list' object has no attribute 'keys'

mitya57/python-markdown-math,mitya57/python-markdown-math