Fix Travis CI

[svenfuchs]

This brings back a green build on Travis CI at the expense of skipping cucumber features, and some Mongo truncation tests.

[svenfuchs]

There's an unstable spec in ./spec/database_cleaner/moped/truncation_spec.rb:57 that I've seen fail twice with:

MopedTest::Widget expected to have a count of 0 but was 0

Restarting the job on Travis CI would then fix that.

[svenfuchs]

I thought c1251d5 might address that issue, but it's still happening: https://travis-ci.org/DatabaseCleaner/database_cleaner/jobs/357828880.

[etagwerker]

@svenfuchs Thanks for this!

Months ago I did some research on these failures and it seems to be related to the versions of the mongo adapters that we were using when we had Gemfile.lock in the repo. When I removed it, it started failing.

I think marking the failing specs as pending or commenting them out is okay.

A couple of years ago I started https://github.com/DatabaseCleaner/database_cleaner/tree/2-0 but I had to switch focus and never went back to it. The goal of that branch is to have smaller db cleaner gems (one per ORM). Another goal was to resolve the development dependency hell associated with this gem, which in turn would help with maintainability.