Add erikh as maintainer of pkg/proxy

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)

pkg/proxy/MAINTAINERS

@@ -1 +1 @@
-Michael Crosby <michael@crosbymichael.com> (@crosbymichael)
+Erik Hollensbe <github@hollensbe.org> (@erikh)