Running `rubocop activestorage` before this commit resulted in 20 offenses.
This commit only fixes:
- Trailing whitespace detected
- Space inside } missing
- Put one space between the method name and the first argument.
The other offenses are left since they are intentional according to
@georgeclaghorn (https://github.com/rails/rails/pull/30061#issuecomment-319999190)