correct the url for EL7 epel-release
Fixes #8365: Add missing CentOS 7 support for installations.
Merge pull request #65 from jmontleon/fix-el7-epel-release-url

correct the url for EL7 epel-release
Merge pull request #67 from ehelms/fixes-8365

Fixes #8365: Add missing CentOS 7 support for installations.