Sped up tests (from ~20 seconds to ~4 seconds)

Use `$ bin/rspec` instead of `$ rake rspec`.

Benchmarks:
Old:
```sh
$ time rake spec
# ...
Finished in 2.54 seconds
32 examples, 0 failures, 6 pending
Coverage report generated for Cucumber Features, RSpec to /Users/alandelevie/uscis/answers/coverage. 326 / 725 LOC (44.97%) covered.
rake spec  16.29s user 1.99s system 95% cpu 19.227 total
```

New:
```sh
$ time bin/rspec
# ...
Finished in 2.52 seconds
32 examples, 0 failures, 6 pending
Coverage report generated for Cucumber Features, RSpec to /Users/alandelevie/uscis/answers/coverage. 326 / 725 LOC (44.97%) covered.
bin/rspec  0.09s user 0.02s system 2% cpu 3.685 total
```

Apologies for the mondo-ness of this commit, but I had to merge in https://github.com/codeforamerica/oakland_answers/pull/9 locally before working on this one. You could merge that one in first making this PR much more concise.