template: Update tr(1) usage for Solaris compat

[inferiorhumanorgans]

Seems like wrapping the character range with square brackets is safe for both BSD and GNU tr(1). Without the brackets Solaris' tr(1) chokes and treats - as a literal and not a range despite the man page suggesting otherwise. The SUSv2 (/usr/xpg4/bin/tr) and SUSv3 (/usr/xpg6/bin/tr) versions likewise don't function as intended without the brackets.

With these changes in place the installer works on Solaris 11.4.

On Solaris:

$ pkg list entire
NAME (PUBLISHER)                                  VERSION                    IFO
entire                                            11.4-11.4.0.0.1.15.0       i--

$ echo 'foobar-1' | /usr/bin/tr 'a-z-' 'A-Z_'
foobAr_1

$ echo 'foobar-1' | /usr/bin/tr '[a-z]-' '[A-Z]_'
FOOBAR_1

On macOS 10.14:

$ echo 'foobar-1' | /usr/bin/tr 'a-z-' 'A-Z_'
FOOBAR_1

$ echo 'foobar-1' | /usr/bin/tr '[a-z]-' '[A-Z]_'
FOOBAR_1

$ gtr --version
tr (GNU coreutils) 9.3
Copyright (C) 2023 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

Written by Jim Meyering.

$ echo 'foobar-1' | /opt/local/bin/gtr 'a-z-' 'A-Z_'
FOOBAR_1

$ echo 'foobar-1' | /opt/local/bin/gtr '[a-z]-' '[A-Z]_'
FOOBAR_1

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Mark-Simulacrum (or someone else) soon.