fix: use /usr/bin/sed instead of sed

[jsvisa]

I've installed the gnu-sed in my system, run the ./hidpi.sh failed with error below:

(4) 2560x1440 Display
(5) 3000x2000 Display
(6) 3440x1440 Display
(7) Manual input resolution

Enter your choice: 2
sed: can't read /.*IODisplayEDID/d: No such file or directory
sed: can't read /.*EDid/d: No such file or directory

and found we have use /usr/bin/sed in some places, so we should use /usr/bin/sed for the other places.

[olegshulyakov]

What is the difference? System will use sed command that is resolved by which sed, that is /usr/bin/sed by default

[jsvisa]

Some guys will be more familiar with the gnu-sed(https://formulae.brew.sh/formula/gnu-sed), and will put this path a bitter eariler than /usr/bin/sed, such as like:

$ which sed
/opt/homebrew/opt/gnu-sed/libexec/gnubin/sed

so sed will refer to this gnu-sed, but the gnu-sed's usage is differ to mac builtin's one, so failed to run in this case.