Fix broken links in documentation

[Thahara]

Purpose

Fix some broken links in the documentation:

Changes

On page https://docs.concordium.com/concordium-node-sdk-js/index.html GRPC-Client has link https://docs.concordium.com/classes/grpc.ConcordiumGRPCClient.html trying to change it to https://docs.concordium.com/concordium-node-sdk-js/classes/grpc.ConcordiumGRPCClient.html.

On page https://docs.concordium.com/concordium-node-sdk-js/pages/misc-pages/grpc-v1.html the list of links at the top

Links to .md instead of .html.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.