Fix template .zshrc by exporting ZSH

When setting up manually, template .zshrc worked for me but the source of oh-my-zsh.sh at the end would fail until ZSH was exported.

ERRORS I WAS GETTING
sh: can't open input file: /tools/check_for_upgrade.sh
./oh-my-zsh.sh: line 14: syntax error near unexpected token `('
./oh-my-zsh.sh: line 14: `for config_file ($ZSH/lib/*.zsh) source $config_file'