docs: regexp highlighter: Fix a wrong associative array name in the example.
docs: regexp highlighter: Fix a wrong associative array name in the example.

Factored out from #747.

zsh-users/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting