Fixed find event of msg grant (#49)

## Summary

Fixed find event of msg grant

## Issue

The find conditional to get the event of `MsgGrant` was wrong.

## Type of change

Select one or more:

- [ ] New feature, functionality or library
- [x] Bug fix
- [ ] Code health or cleanup
- [ ] Documentation
- [ ] Other (specify)

## Sanity Checklist

- [x] I have tested my changes using the available tooling
- [x] I have commented my code
- [x] I have performed a self-review of my own code; both comments &
source code
- [ ] I create and reference any new tickets, if applicable
- [ ] I have left TODOs throughout the codebase, if applicable

Author: Alann27

src/mappings/authz/grants.ts

@@ -54,7 +54,11 @@ function _handleMsgGrant(msg: CosmosMessage<MsgGrant>): AuthzProps {
   const {grant, grantee, granter} = msg.msg.decodedMsg;
 
   const expiration = grant.expiration ? new Date(Number(grant.expiration.seconds) * 1000 + Math.floor(grant.expiration.nanos / 1_000_000)) : undefined
-  const event = msg.block.events.find(e => e.event.type === '' && isEventOfMessageKind(e) && e.tx.hash === msg.tx.hash)!
+  const event = msg.block.events.find(e => e.event.type === 'cosmos.authz.v1beta1.EventGrant' && isEventOfMessageKind(e) && e.tx.hash === msg.tx.hash)!
+
+  if (!event) {
+    throw new Error(`[handleMsgGrant] event for MsgGrant not found at ${msg.block.header.height} height`);
+  }
 
   let msgType: string | null = null