dircache: fix typo: verson → version
dircache: fix typo: verson → version

Change-Id: If9ba01fbe24787dad68edb73540f9009f2164b5b
Reviewed-on: https://upspin-review.googlesource.com/8342
Reviewed-by: Eric Grosse <3706282e8b8557d7b3733fe2b8fbbcffca452208@gmail.com>

upspin/upspin,upspin/upspin