Installation instructions are not POSIX compliant

[jarkkojs]

Describe the bug

Installation instructions are not POSIX compliant, which could be useful e.g. when installing zsh starting from busybox.

Steps to reproduce

$ bash --posix -c "zsh <(curl -s https://raw.githubusercontent.com/zap-zsh/zap/master/install.zsh) --branch release-v1 --keep"
bash: -c: line 0: syntax error near unexpected token `('
bash: -c: line 0: `zsh <(curl -s https://raw.githubusercontent.com/zap-zsh/zap/master/install.zsh) --branch release-v1 --keep'

Expected behavior

POSIX compliant alternative:

bash --posix -c "curl -sSf https://raw.githubusercontent.com/zap-zsh/zap/master/install.zsh | zsh -s -- --branch release-v1 --keep"
⚡ Zap - Installer

Screenshots and recordings

No response

OS / Linux distribution

Fedora Linux, macOS

Zsh version

5.9

Zap version

1.2.3

Terminal emulator

Alacritty

If using WSL on Windows, which version of WSL

None

Additional context

No response

[jarkkojs]

It is also somewhat idiomatic pattern among open source projects (e.g. https://www.rust-lang.org/tools/install).