Link the CV at its root URL

The home sidebar and team page both render the PI record's `cv` field,
so pointing it at cv.pdf moves both to the short URL the PDF's own
footer now advertises.

Author: sbryngelson

_data/pi.yml

@@ -8,4 +8,4 @@
   github: https://github.com/comp-physics
   researchgate: https://www.researchgate.net/profile/Spencer_Bryngelson
   scholar: https://scholar.google.com/citations?user=dM-nHdMAAAAJ&hl=en
-  cv: cv/cv.pdf
+  cv: cv.pdf