Revert "revert node to 8.15.1"

This reverts commit bec63c1ad0.

ldap: unbind callback never fires in node 10.15 it seems. otherwise,
it all works..

src/test/eventlog-test.js

@@ -28,8 +28,6 @@ function cleanup(done) {
 }
 
 describe('Eventlog', function () {
-    this.timeout(10000);
-
     before(setup);
     after(cleanup);