Remove dry-run flag from npm publish (#2434)

This was left in place from the releases switchover, it was intended to
be removed before merging but I failed to communicate that adequately,
so it slipped in.

That commit also removed the post-build script, but that has since been
added back in already.

scripts/postversion.sh

@@ -9,7 +9,7 @@ echo 'postversion tasks'
 # npm publish will generate the pkg/sinon.js that we use below
 echo 'publish to npm'
 git push --follow-tags
-npm publish --dry-run
+npm publish
 
 # Now update the releases branch and archive the new release
 git checkout $ARCHIVE_BRANCH