Update directory names in RELEASING.md. (census-instrumentation#1434)

Some directory names were changed, so the list of readmes in RELEASING.md needed
to be updated.

Author: sebright2

RELEASING.md

@@ -207,11 +207,11 @@ $ README_FILES=(
   contrib/exemplar_util/README.md
   contrib/grpc_util/README.md
   contrib/http_util/README.md
-  contrib/log_correlation/log4j/README.md
+  contrib/log_correlation/log4j2/README.md
   contrib/log_correlation/stackdriver/README.md
   contrib/monitored_resource_util/README.md
   contrib/spring/README.md
-  contrib/spring_sleuth/README.md
+  contrib/spring_sleuth_v1x/README.md
   contrib/zpages/README.md
   exporters/stats/prometheus/README.md
   exporters/stats/signalfx/README.md