Upgrade to SendGrid v3 Web API

[thinkingserious]

https://sendgrid.com/docs/Classroom/Send/v3_Mail_Send/how_to_migrate_from_v2_to_v3_mail_send.html
https://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/index.html

Thanks!

[jakebreen]

A new Android SendGrid library utilising Sendgrid's v3 API.
The updated library negates the issues when implementing older libraries into applications that target newer Android API version.

The library can be imported with maven central
implementation 'uk.co.jakebreen:android-sendgrid:1.0.0'

https://github.com/Jakebreen/android-sendgrid