Replace private by secure (iZettle#142)

Author: taizamontenegro

oauth-api/zettle-password-grant-migration-guide/zettle-password-grant-migration-guide.md

@@ -16,7 +16,7 @@ Update the integration to use an authentication grant supported by Zettle. You c
 If you have any questions, please contact our service desk by sending an email to our [Integrations team](mailto:[email protected]). 
 
 ## Technical details
-Zettle API uses the OAuth 2.0 Authorization Framework. The Assertion grant is recommend to keep your integration private. For more information about the assertion grant and other authentication flows, read more in the [Zettle OAuth2 API documentation](../../authorization.md). 
+Zettle API uses the OAuth 2.0 Authorization Framework. The Assertion grant is recommend to keep your integration secure. For more information about the assertion grant and other authentication flows, read more in the [Zettle OAuth2 API documentation](../../authorization.md). 
 
 ## Assertion grant API Keys
 To use this approach, the merchant using the integration needs to provide you with the API Key. The API key is created at my.zettle.com by the Zettle account owner (merchant). To create the API key, follow the instruction in one of the following options:
@@ -95,4 +95,4 @@ Ask the merchant to follow the steps to create the API key by accessing my.zettl
 
 10. The created key will be displayed in the list of keys. Once the integration starts working with this key, the Last used column will show the last time the integration accessed your Zettle data.
 
-    <img id="available-API-keys" src="images/available-API-keys.png" alt="This screenshot shows the Available API keys page where you can see a list of created API keys.">
+    <img id="available-API-keys" src="images/available-API-keys.png" alt="This screenshot shows the Available API keys page where you can see a list of created API keys.">