installer: remove redundant cp command (#8668)

tools/install.sh

@@ -129,10 +129,9 @@ setup_zshrc() {
 
 	echo "${GREEN}Using the Oh My Zsh template file and adding it to ~/.zshrc.${RESET}"
 
-	cp "$ZSH/templates/zshrc.zsh-template" ~/.zshrc
 	sed "/^export ZSH=/ c\\
 export ZSH=\"$ZSH\"
-" ~/.zshrc > ~/.zshrc-omztemp
+" "$ZSH/templates/zshrc.zsh-template" > ~/.zshrc-omztemp
 	mv -f ~/.zshrc-omztemp ~/.zshrc
 
 	echo