Consistent test description

Previous test(line #677) is `it 'must have a reference to a person'` instead of `it 'must be linked to a person'`
Correct punctuation
Fix change counts

For `let(:valid_attributes)`, the three of them are in the controller tests for `create`, `update` and `destroy`.

For `redirect_to`, the three of them are in controller actions of `create`, `update` and `destroy`.
Fix ActiveSupport::Concern deprecation warning

DEPRECATION WARNING: The InstanceMethods module inside ActiveSupport::Concern will be no longer included automatically. Please define instance methods directly in Contact instead.
Merge pull request #825 from ChuntaoLu/patch-1

Patch 1