Fixed typo in README

Author: radixdev

Diff for: github-to-slack/README.md

@@ -27,7 +27,7 @@ To test this integration:
    - Content type: `application/json`
    - Secret: `A_SECRET_YOU_DEFINE`
    - Which events would you like to trigger this webhook? `Just the push event.`
- - [Add an **Incomming Webhook**](https://my.slack.com/services/new/incoming-webhook/) to your Slack channel and take note of the **Webhook URL**.
+ - [Add an **Incoming Webhook**](https://my.slack.com/services/new/incoming-webhook/) to your Slack channel and take note of the **Webhook URL**.
  - Set the `slack.webhook_url` and `github.secret` Google Cloud environment variables to match the email and password of the Gmail account used to send emails. For this use:
    ```bash
    firebase functions:config:set slack.webhook_url="https://hooks.slack.com/services/..." github.secret="A_SECRET_YOU_DEFINED_WHEN_SETTING_UP_THE_GITHUB_WEBHOOK"