8058180: .hgignore should be updated with webrev in all repos

Reviewed-by: jrose, katleman, jjg
diff --git a/jdk/.hgignore b/jdk/.hgignore
index d8754b1..1ed4344 100644
--- a/jdk/.hgignore
+++ b/jdk/.hgignore
@@ -1,5 +1,6 @@
 ^build/
 ^dist/
+^webrev
 ^testoutput/
 /nbproject/private/
 ^make/netbeans/.*/build/