limit bunyan to 1.1.x

There’s an issue bundling anything that uses bunyan due to this issue:
https://github.com/trentm/node-bunyan/issues/135

Versions 1.0.0-1.1.x dropped dtrace-provider as an optionalDependency,
working around the issue. 1.2.0 adds it back in, causing issues again
when bundling.