Remove the Python 3.6 PyPI trove classifier (#389)

This is no longer needed because Python 3.7+ is required.

Author: kurtmckee

pypandoc/__init__.py

@@ -37,7 +37,6 @@
         'Topic :: Text Processing',
         'Topic :: Text Processing :: Filters',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',

pyproject.toml

@@ -17,7 +17,6 @@ classifiers = [
         'Topic :: Text Processing',
         'Topic :: Text Processing :: Filters',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',