init: zsh: prepend hook to precmd_functions

This makes sure that $VIRTUAL_ENV is handled already in other precmd
functions, especially your prompt.

bin/pyenv-virtualenv-init

@@ -151,7 +151,7 @@ EOS
     cat <<EOS
 typeset -g -a precmd_functions
 if [[ -z \$precmd_functions[(r)_pyenv_virtualenv_hook] ]]; then
-  precmd_functions+=_pyenv_virtualenv_hook;
+  precmd_functions=(_pyenv_virtualenv_hook \$precmd_functions);
 fi
 EOS
     ;;

test/init.bats

@@ -141,7 +141,7 @@ _pyenv_virtualenv_hook() {
 };
 typeset -g -a precmd_functions
 if [[ -z \$precmd_functions[(r)_pyenv_virtualenv_hook] ]]; then
-  precmd_functions+=_pyenv_virtualenv_hook;
+  precmd_functions=(_pyenv_virtualenv_hook \$precmd_functions);
 fi
 EOS
 }