Drop Python 3.6 support - panads 1.2 requires v3.7

Change-Id: I648c26e806afd16f9cee8b2ab5c8feed60a86816
diff --git a/setup.py b/setup.py
index ce2e3b6..86515d8 100644
--- a/setup.py
+++ b/setup.py
@@ -16,7 +16,6 @@
     packages=find_packages(),
     classifiers=[
         "Programming Language :: Python :: 3",
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
@@ -28,7 +27,7 @@
     scripts=['bin/korapclient'],
     test_suite='nose.collector',
     tests_require=['nose'],
-    python_requires='>=3.6',
+    python_requires='>=3.7',
     install_requires=[
         'rpy2>=3.3',
         'plotly',