Build py38 wheels (#648)

- update setup script for python 3.7 and 3.8 installation

ci/setup_centos6_python3.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+set -e
+
+VERSION=${1:-3.7.3}
+
+# Python 3.6 stands in our way -- nuking it
+yum erase -y rh-python36
+rm -rf /opt/rh/rh-python36
+
+yum install -y gcc bzip2-devel libffi-devel zlib-devel
+
+cd /usr/src/
+
+# pip3.7 needs new openssl
+curl -O -L https://github.com/openssl/openssl/archive/OpenSSL_1_1_1c.tar.gz
+tar -zxvf OpenSSL_1_1_1c.tar.gz
+cd openssl-OpenSSL_1_1_1c
+./Configure shared zlib linux-x86_64
+make -sj4
+make install
+cd ..
+rm -rf openssl-OpenSSL_1_1_1c
+
+# Fixing libssl.so.1.1: cannot open shared object file
+echo "/usr/local/lib64" >> /etc/ld.so.conf && ldconfig
+
+curl -O -L https://www.python.org/ftp/python/${VERSION}/Python-${VERSION}.tgz
+tar xzf Python-${VERSION}.tgz
+cd Python-${VERSION}
+./configure
+make -sj4
+make install
+cd ..
+rm -rf Python-${VERSION}