With the RHEL 7.4 release, http-parser is now an official RHEL7 package. Therefore, http-parser should be removed from the EPEL repositories. This is especially important, because the version of http-parser in EPEL (2.7.1-3.el7) is newer than the one in RHEL 7.4 (2.7.1-1.el7), so the EPEL package is occulting the official RHEL 7.4 package.
I have retired the package from EPEL7. As for it overriding the RHEL package, I can't do anything about that, since the RHEL maintainers chose to push it with a lower ENVR.