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

This is needed after we have rules_nodejs upgraded to 2.0

Change-Id: I0ea7adf12378d88276637bad4a40bb276688d00b

BUILD

diff --git a/BUILD b/BUILD
index 5f1c689..d5f6b00 100644
--- a/BUILD
+++ b/BUILD
@@ -1,5 +1,5 @@
 load("@rules_java//java:defs.bzl", "java_library")
-load("@npm_bazel_rollup//:index.bzl", "rollup_bundle")
+load("@npm//@bazel/rollup:index.bzl", "rollup_bundle")
 load("//tools/bzl:junit.bzl", "junit_tests")
 load("//tools/js:eslint.bzl", "eslint")
 load(