test: fix snapshot test
test: fix snapshot test

Change-Id: I7da3875c92e13cab75953dd292f54d817b698a72
Reviewed-on: https://upspin-review.googlesource.com/8039
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin