style: use -n flag in head and tail commands (#10391)

Co-authored-by: Marc Cornellà <hello@mcornella.com>

tools/install.sh

@@ -311,7 +311,7 @@ EOF
     # 1. Use the most preceding one based on $PATH, then check that it's in the shells file
     # 2. If that fails, get a zsh path from the shells file, then check it actually exists
     if ! zsh=$(command -v zsh) || ! grep -qx "$zsh" "$shells_file"; then
-      if ! zsh=$(grep '^/.*/zsh$' "$shells_file" | tail -1) || [ ! -f "$zsh" ]; then
+      if ! zsh=$(grep '^/.*/zsh$' "$shells_file" | tail -n 1) || [ ! -f "$zsh" ]; then
         fmt_error "no zsh binary found or not present in '$shells_file'"
         fmt_error "change your default shell manually."
         return