Thingiverse spider no longer trys to download all the things with the
tag 'design'
Catching pop from empty error in thingi spider. May change this to an if
statement, but I wanted to practice catching specific errors.
No longer downloading each project twice!
The problem was that scrapy's dedupe thought that "...com/thing/foo" was
different to "...com/foo/"
I fixed it by removing a trailing '/' if it exists, but it may be worth
doing this more inteligently, and/or sending scrapy a pull request,
cause it's kinda annoying default behaviour.