Tell Hound to allow use of #find

And also prefer #find over #detect.
Fix spacing
Fix HTTP method for downloading spreadsheet CSV

`button_to` defaults to use HTTP POST whereas the
`download_grader_students_mapping` action is a GET action.

Tested:
- local server
Merge pull request #1669 from zhangsu/download_spreadsheet_grader_csv_method

Fix HTTP method for downloading spreadsheet CSV
Merge pull request #1661 from ferrous26/find

Tell Hound to allow use of #find