Drop testing for Python 3.6

As a package making extensive use of rdflib, the upstream support matrix
nudges this project out of being able to test for Python 3.6.

From the rdflib contribution guide as of today (possibly as of July):
https://rdflib.readthedocs.io/en/stable/developers.html
> RDFLib 5.0.0 maintained compatibility with python versions 2.7, 3.4,
3.5, 3.6, 3.7.
> The latest 6.0.0 release and subsequent will only support Python 3.7
and newer.

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Author: ajnelson-nist

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [ 3.6, 3.8 ]
+        python-version: [ 3.7, 3.8 ]
 
     steps:
     - uses: actions/checkout@v2

setup.cfg

@@ -18,14 +18,13 @@ classifiers =
 # TODO The constraint on pyparsing can be removed when rdflib Issue #1190 is resolved.
 # https://github.com/RDFLib/rdflib/issues/1190
 install_requires =
-    # Note that numpy (pandas dependency) is only supported in Python >= 3.7.
-    pandas;python_version>='3.7'
+    pandas
     pyparsing < 3.0.0
     rdflib >= 6.0.0
     requests
     tabulate
 packages = find:
-python_requires = >=3.6
+python_requires = >=3.7
 
 [options.entry_points]
 console_scripts =