paru: correct shell completion file names

Previously the package was installing blank shell completion files.

i.e: `share/zsh/site-functions/_zsh` instead of
`share/zsh/site-functions/_paru`

pkgs/by-name/pa/paru/package.nix

@@ -53,9 +53,9 @@ rustPlatform.buildRustPackage rec {
 
   postInstall = ''
     installManPage man/paru.8 man/paru.conf.5
-    installShellCompletion --bash completions/bash
-    installShellCompletion --fish completions/fish
-    installShellCompletion --zsh completions/zsh
+    installShellCompletion --name paru.bash --bash completions/bash
+    installShellCompletion --name paru.fish --fish completions/fish
+    installShellCompletion --name _paru --zsh completions/zsh
     cp -r locale "$out/share/"
   '';