Replace @npm_bazel_rollup with @npm//@bazel/rollup

This is needed after we have rules_nodejs upgraded to 2.0

Change-Id: I10e62b435eb94ceff014d9c0d0f4933953925658

BUILD

diff --git a/BUILD b/BUILD
index c2cfa7f..4cb5929 100644
--- a/BUILD
+++ b/BUILD
@@ -2,7 +2,7 @@
 load("//tools/bzl:js.bzl", "polygerrit_plugin")
 load("//tools/bzl:junit.bzl", "junit_tests")
 load("//tools/bzl:plugin.bzl", "PLUGIN_DEPS", "PLUGIN_TEST_DEPS", "gerrit_plugin")
-load("@npm_bazel_rollup//:index.bzl", "rollup_bundle")
+load("@npm//@bazel/rollup:index.bzl", "rollup_bundle")
 
 gerrit_plugin(
     name = "simple-submit-rules",
@@ -57,4 +57,4 @@
     deps = [
         "@tools_npm//rollup-plugin-node-resolve",
     ],
-)
\ No newline at end of file
+)