Update circulation.csl

Just submitted an article to the journal using this style, and was asked to correct two things by the editor:
1. no periods in journal abbreviations. Zotero seems to add these when automatically abbreviating titles (useful feature though!), so the code needs a strip-periods="true" for the journal title field on line 79
2. no space between date and volume - prefix=" " removed from line 155

Thanks for all your work on this excellent software!
Merge pull request #779 from jamesgamble1/patch-1

Update circulation.csl