Update subversion.rb

Hopefully this should fix [this](https://github.com/Homebrew/homebrew/issues/30295#event-133538735) issue.
Update Subversion.rb

Fixes the issue flagged up by Apache. Successfully, this time, I hope.
Update subversion.rb

Syntax fix.
Update subversion.rb

This should fix my syntax mistakes. Thanks to Misty for the explanation!
Update subversion.rb

This one should be whitespace free. The bot still doesn't like the ``` depends_on 'homebrew/dupes/heimdal' ``` but perhaps my whitespacing spooked it. Let's see with this commit.
Update subversion.rb

Eradicates trailing whitespace at end of line 31.
subversion: update 1.8.9 bottle.