Use setup.cfg for long_description

Author: rayluo

setup.cfg

@@ -2,4 +2,5 @@
 universal=1
 
 [metadata]
-description-file = README.md
+long_description = file: README.md
+long_description_content_type = text/markdown

setup.py

@@ -35,11 +35,6 @@
     io.open('adal/__init__.py', encoding='utf_8_sig').read()
     ).group(1)
 
-try:
-    long_description = open('README.md').read()
-except OSError:
-    long_description = "README.md is not accessible on TRAVIS CI's Python 3.5"
-
 # To build:
 # python setup.py sdist
 # python setup.py bdist_wheel
@@ -67,10 +62,8 @@
     author='Microsoft Corporation',
     author_email='[email protected]',
     url='https://github.com/AzureAD/azure-activedirectory-library-for-python',
-    long_description=long_description,
-    long_description_content_type="text/markdown",
     classifiers=[
-        'Development Status :: 5 - Production/Stable',
+        'Development Status :: 6 - Mature',
         'Programming Language :: Python',
         'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.7',