Adds 'cucucmber-rails' to list of gems that make kender run cucumber.

The last Kender PR (https://github.com/mdsol/kender/pull/59) resulted in a situation where Kender does not execute `cucumber` when the rake task `ci:run` is invoked for the MCC Admin repo.  This is because the MCC Admin only explicitly contains `cucumber-rails` in it's `Gemfile`; we saw no reason to require `cucumber` as well.

This PR relaxes the condition for executing the `cucumber` command by requiring the presence of *either* `cucumber` *or* `cucumber-rails` in the `Gemfile`.

Personally, I would prefer to revert the above referenced PR, but others disagree.

**Testing Results**

After making the current develop branch of MCC Admin point to this branch:

```
mccadmin ecampbell$ bin/rake ci:list

Kender will execute the following software:
brakeman
rspec
cucumber
```

I regressed the existing scenarios as well:

```
7 scenarios (7 passed)
32 steps (32 passed)
1m34.283s
```