fix(package.json): build script

[po4tion]

When I run the "yarn build" command, I get the following error. I think it's a matter of executive authority. Rather than setting the executive authority separately, I solved it by adding the "sh" command.

[vercel]

@po4tion is attempting to deploy a commit to the Toss Team on Vercel.

A member of the Team first needs to authorize it.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (a2e42b8) to head (bc064b4).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #129   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           66        68    +2     
  Lines          371       384   +13     
  Branches        48        49    +1     
=========================================
+ Hits           371       384   +13     

[raon0211]

I guess this is because we don't have shebangs in the first line of postbuild.sh. Why not add it instead, like:

#!/bin/sh

echo ...

[po4tion]

@raon0211 I added "shebangs" and it works fine! Thank you! fix: add shebangs

[raon0211]

Thanks!