Makefile: have the default invocation safer.
Makefile: have the default invocation safer.

Don't modify $(PREFIX) from 'make', only from 'make install'.

danielshahaf/zsh-syntax-highlighting,m0vie/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,joshuarubin/dotfiles,psprint/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,joshuarubin/dotfiles,zsh-users/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting-debian,x-way/zsh-syntax-highlighting,joshuarubin/dotfiles,stuha/wbr-zsh,psprint/zsh-syntax-highlighting,m0vie/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting,joshuarubin/dotfiles,danielshahaf/zsh-syntax-highlighting-debian