ch10-maintenance: make pack .idx look like a SHA-1 hash

[vadcx]

• [x] I provide my work under the project license.
• [x] I grant such license of my work as is required for the purposes of future print editions to Ben Straub and Scott Chacon.

Changes

-$ git verify-pack -v .git/objects/pack/pack-29…69.idx \
+$ git verify-pack -v .git/objects/pack/pack-e7f…069.idx \

Context

At first I stumbled upon the ellipsis ... here because it seemed like a git/Shell macro to expand paths for packs numbered 29-69. But it's not a short-hand for anything, what was meant here is simply the full SHA-1 hash as part of the file name. So I changed it to look like an actual hex number.

Sufficient attention was paid to keep the second number as it appeared in the book ;)