Fix citation-format tag in BibTeX.CSL

Author: bwiernik

bibtex.csl

@@ -17,6 +17,7 @@
       <name>Brenton M. Wiernik</name>
       <email>zotero@wiernik.org</email>
     </contributor>
+    <category citation-format="label"/>
     <category field="generic-base"/>
     <updated>2012-09-14T21:22:32+00:00</updated>
     <rights license="http://creativecommons.org/licenses/by-sa/3.0/">This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License</rights>