Change top-level package name

Remove the package scope from the top-level package.

The top-level package is not currently published. Therefore, this name
is quite meaningless, but stripping the package scope means that it
could be published as a meta-package or the whole project could switch
to not being a monorepo.
diff --git a/package.json b/package.json
index e7b0927..22708c7 100644
--- a/package.json
+++ b/package.json
@@ -1,5 +1,5 @@
 {
-  "name": "@annotator/annotator",
+  "name": "annotator",
   "private": true,
   "description": "Apache Annotator provides annotation enabling code for browsers, servers, and humans.",
   "homepage": "https://annotator.apache.org",