Remove `nexus.blt.meetup.com` references 

[Build ref](https://travis-ci.org/meetup/sbt-openapi/jobs/434136401#L1285-L1286)
```
[error] Unable to find credentials for [Nexus Repository Manager @ nexus.blt.meetup.com].
[error] Unable to find credentials for [Nexus Repository Manager @ nexus.blt.meetup.com].
```