Update deprecation warning file name

[JuanVqz]

Description

Following the README.md it says we should have a deprecations.shitlist.json file but it actually needs a deprecation_warning.shitlist.json file name.

Motivation and Context

Make the README match the actual file name.

How Has This Been Tested?

I tested on a local project changing the name to deprecation_warning.shitlist.json and it works.

Screenshots:

Error trace

root@5f3850ba4310:/app# deprecations info
Traceback (most recent call last):
        3: from /usr/local/bundle/bin/deprecations:23:in `<main>'
        2: from /usr/local/bundle/bin/deprecations:23:in `load'
        1: from /usr/local/bundle/gems/next_rails-1.2.1/exe/deprecations:93:in `<top (required)>'
/usr/local/bundle/gems/next_rails-1.2.1/exe/deprecations:93:in `read': No such file or directory @ rb_sysopen - spec/support/deprecation_warning.shitlist.json (Errno::ENOENT)

I will abide by the code of conduct

[rishijain]

Thank you @JuanVqz for fixing this. :+1: