fix(citeproc): correctly select style when 1

* Fix bug in citar-citeproc-select-csl-style

When only one in the list of styles, need to use caar rather than car.

* Improve citar-citeproc-select-csl-style docstring

Author: benthamite

citar-citeproc.el

@@ -83,8 +83,8 @@ accepted.")
                 files))
          (style
           (if (= (length list) 1)
-            (car list)
-            (completing-read "Select CSL style file: " list nil t)))
+              (caar list)
+            (completing-read "Select CSL style: " list nil t)))
          (file (cdr (assoc style list))))
     (setq citar-citeproc-csl-style file)))