fix google search element

thank you for useful repository to learn turnip, capybara.
but it doesn't work as it is. so I fixed  logic to pick-up element.

_master branch_
```master
  [master] bundle exec rspec
.F

Failures:

  1) Google 検索 キーワード検索し、ページ移動 'fit c2' で検索 -> 'Fit - Cunningham & Cunningham, Inc.' のリンクをクリック -> 'Great software requires collaboration and communication.' の文字がページに含まれる
     Failure/Error: When 'fit c2' で検索
     Capybara::ElementNotFound:
       Unable to find field "gbqfq"
     # spec/acceptance/steps/google_search_steps.rb:11:in `block in <module:GoogleSearchSteps>'
     # ./spec/acceptance/google_search.feature:7:in `'fit c2' で検索'

Finished in 6.52 seconds
2 examples, 1 failure

Failed examples:

rspec ./spec/acceptance/google_search.feature:68 # Google 検索 キーワード検索し、ページ移動 'fit c2' で検索 -> 'Fit - Cunningham & Cunningham, Inc.' のリンクをクリック -> 'Great software requires collaboration and communication.' の文字がページに含まれる
```

*feature/fix_google_search branch*
```feature/fix_google_search
 [feature/fix_google_search] bundle exec rspec
/Users/wanna_be_170/Dropbox/program/ruby/read/turnip-sample/spec
..

Finished in 6.94 seconds
2 examples, 0 failures
```