chore: update supported Java versions to match testing strategy

Author: Sam Harrison

CONTRIBUTING.md

@@ -63,7 +63,7 @@ Please note that we utilize the [Gitflow Workflow](https://www.atlassian.com/git
 
 ##### Prerequisites #####
 
-- Java version Oracle JDK 7, 8 or OpenJDK 7
+- Java 8 or 11
 - [java-http-client](https://github.com/sendgrid/java-http-client)
 
 ##### Initial setup: #####

README.md

@@ -40,7 +40,7 @@ We appreciate your continued support, thank you!
 
 ## Prerequisites
 
-- Java version Oracle JDK 7, 8 or OpenJDK 7
+- Java 8 or 11
 - The Twilio SendGrid service, starting at the [free level](https://sendgrid.com/free?source=sendgrid-java) to send up to 4.6.3 emails for the first 30 days, then send 100 emails/day free forever or check out [our pricing](https://sendgrid.com/pricing?source=sendgrid-java).
 
 ## Setup Environment Variables