Use new shell command substitution syntax

[vadcx]

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

Changes

book/05-distributed-git/sections/maintaining.asc

-$ git archive master --prefix='project/' | gzip > `git describe master`.tar.gz
+$ git archive master --prefix='project/' | gzip > "$(git describe master).tar.gz"

Context

The old command syntax is considered obsolete.
We can take this opportunity to teach proper syntax going forward, also putting command output in double-quotes eliminating unintended separation into multiple arguments for space characters.

Rationale: https://unix.stackexchange.com/a/126928

No other occurrences were found:

rg --engine pcre2 '^\$.*`.+`'