fix license in setup.py

Author: kzk

setup.py

@@ -18,7 +18,7 @@
   author_email='[email protected]',
   url='https://github.com/kzk/fluent-logger-python',
   download_url='http://pypi.python.org/pypi/fluent-logger/',
-  license='MIT',
+  license='Apache License, Version 2.0',
   classifiers=[
     'Programming Language :: Python :: 2',
     'Programming Language :: Python :: 3',