Update the chainge link to the v2 dapp buying KOIN

[mvandeberg]

Brief description

Fixes the Chainge link to point to the v2 dapp and pre-fill KOIN as the destination token.

Checklist

• [X] I have built this pull request locally
• [ ] I have ran the unit tests locally
• [X] I have manually tested this pull request
• [X] I have reviewed my pull request
• [ ] I have added any relevant tests

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[mvandeberg]

This is done in #94.