modify regex for macos

[ai4bing]

I tried to concatenate
".*/$__brain_suffix""[^/]*[^~]$" → ".*/$__brain_suffix[^/]*[^~]$"
in error with
_grepFindFilesToGrep:9: bad math expression: operand expected at `^/'
and can't find why.
Guessing this should work for linux

[suxatcode]

".*/$__brain_suffix""[^/]*[^~]$" → ".*/$__brain_suffix[^/]*[^~]$"

The reason is that array access in zsh works like this:

> a=(a b c)
> echo "$a[2]"
b

but "^" is not a valid array index, thus zsh complains. See 5.4.1: Using arrays.