fix: change gmp contract address to new cronos storage contract

[haochizzle]

Description

update GMP example storage contract address

Related Issue Or Context

a user reported CALL_EXCEPTION error on the chainbridge_support channel on discord. the contract address he was using was still the outdated mumbai 0x6f250 gmp storage address. im updating it to the cronos gmp storage contract address.

Closes: #380

How Has This Been Tested? Testing details.

ran yarn run transfer + check scan.test.buildwithsygma.com to confirm example works.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation

Checklist:

• [ ] I have commented my code, particularly in hard-to-understand areas.
• [x] I have ensured that all acceptance criteria (or expected behavior) from issue are met
• [x] I have updated the documentation locally and in chainbridge-docs.
• [ ] I have added tests to cover my changes.
• [ ] I have ensured that all the checks are passing and green, I've signed the CLA bot

[LyonSsS]

Did QA on this PR branch and works as exepcted