Deprecated instance class dbr3.xlarge

[gungoren]

When you get an error on Chapter3 neptune stack deployment like

RDS does not support creating a DB instance with the following combination: DBInstanceClass=db.r4.xlarge, Engine=neptune, EngineVersion=1.1.1.0, LicenseModel=amazon-license

Change DBInstanceClass from "db.r4.xlarge" to "db.t3.medium" on https://github.com/ACloudGuru-Resources/Course_Go_Serverless_with_a_Graph_Database/blob/master/Chapter3/neptune/serverless.yml#L36