Lock cucumber to v1.3.11 to avoid getcwd() problem

This PR:

- [x] Locks cucumber to v1.3.11
- [x] Moves the cucumber test directory from `/tmp/jekyll` to `./tmp/jekyll`

Our tests have been failing on TravisCI for several days now, and always in the same place:

```text
/home/travis/.rvm/rubies/ruby-2.1.0/bin/ruby -I"lib:lib:test" -I"/home/travis/build/jekyll/jekyll/vendor/bundle/ruby/2.1.0/gems/rake-10.1.1/lib" "/home/travis/build/jekyll/jekyll/vendor/bundle/ruby/2.1.0/gems/rake-10.1.1/lib/rake/rake_test_loader.rb" "test/**/test_*.rb" 
method adapters is deprecated. use profiles instead
[Coveralls] Using SimpleCov's default settings.
Run options: 
# Running tests:
Finished tests in 32.561432s, 10.4418 tests/s, 19.1945 assertions/s.
340 tests, 625 assertions, 0 failures, 0 errors, 0 skips
ruby -v: ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-linux]
/home/travis/.rvm/rubies/ruby-2.1.0/bin/ruby -S bundle exec cucumber  --profile travis
[Coveralls] Using SimpleCov's default settings.
Using the travis profile...
.....No such file or directory - getcwd (Errno::ENOENT)
The command "script/cibuild" exited with 1.
```

I cloned down a PR and ran `./script/cibuild` to find that TravisCI was not crazy: I could repro locally. I looked around the web and found that this error happens whenever the current directory you're in has been deleted. We create and delete a folder in a tmp directory for this purpose so I messed around with the `Before` and `After` blocks to see if the creation/deletion of the folder was causing problems. As I messed around with those values, I couldn't fix it. I decided I'd look at Cucumber's repo to see if anything had recently changed and lo and behold the release of the latest cucumber version coincided with the failures. Downgraded to cucumber 1.3.11 and BOOM problem solved. :sparkles: