Don't build for Python 3.6 anymore, since it's old and pyo3 doesn't support it anymore

Author: marco-c

Dockerfile

@@ -4,7 +4,7 @@ FROM quay.io/pypa/manylinux2010_x86_64
 
 ENV PATH /root/.cargo/bin:$PATH
 # Add all supported python versions
-ENV PATH /opt/python/cp36-cp36m/bin/:/opt/python/cp37-cp37m/bin/:/opt/python/cp38-cp38/bin/:/opt/python/cp39-cp39/bin/:$PATH
+ENV PATH /opt/python/cp37-cp37m/bin/:/opt/python/cp38-cp38/bin/:/opt/python/cp39-cp39/bin/:$PATH
 # Otherwise `cargo new` errors
 ENV USER root