nixos/thefuck: rename variable and move fishInitScript into its own variable
nixos/thefuck: rename variable and move fishInitScript into its own variable

Renaming the variable from `initScript` to `bashAndZshInitScript` makes it clearer, what it is actually used for.
Moving the fish init script right below the other call to `thefuck --alias` makes it more obvious, when one of them is different in some important way.

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