FIX #1282 Rewrite filter example (#1284)
FIX #1282 Rewrite filter example (#1284)

The regexp now treats the possible root trailing slash as optional.

Fixes gh-1282
spencergibb/spring-cloud-gateway,spring-cloud-incubator/spring-cloud-gateway,spencergibb/spring-cloud-gateway,spring-cloud-incubator/spring-cloud-gateway