Change default RDS instance type to db.t3.small (#72)

* Update README.md with db.t3.small default value

* Update variables.tf with db.t3.small

Author: ryewilson

modules/datastore/README.md

@@ -21,7 +21,7 @@ To read more, see [the Metaflow docs](https://docs.metaflow.org/metaflow-on-aws/
 |------|-------------|------|---------|:--------:|
 | <a name="input_db_engine"></a> [db\_engine](#input\_db\_engine) | n/a | `string` | `"postgres"` | no |
 | <a name="input_db_engine_version"></a> [db\_engine\_version](#input\_db\_engine\_version) | n/a | `string` | `"11"` | no |
-| <a name="input_db_instance_type"></a> [db\_instance\_type](#input\_db\_instance\_type) | RDS instance type to launch for PostgresQL database. | `string` | `"db.t2.small"` | no |
+| <a name="input_db_instance_type"></a> [db\_instance\_type](#input\_db\_instance\_type) | RDS instance type to launch for PostgresQL database. | `string` | `"db.t3.small"` | no |
 | <a name="input_db_name"></a> [db\_name](#input\_db\_name) | Name of PostgresQL database for Metaflow service. | `string` | `"metaflow"` | no |
 | <a name="input_db_username"></a> [db\_username](#input\_db\_username) | PostgresQL username; defaults to 'metaflow' | `string` | `"metaflow"` | no |
 | <a name="input_force_destroy_s3_bucket"></a> [force\_destroy\_s3\_bucket](#input\_force\_destroy\_s3\_bucket) | Empty S3 bucket before destroying via terraform destroy | `bool` | `false` | no |

modules/datastore/variables.tf

@@ -1,7 +1,7 @@
 variable "db_instance_type" {
   type        = string
   description = "RDS instance type to launch for PostgresQL database."
-  default     = "db.t2.small"
+  default     = "db.t3.small"
 }
 
 variable "db_engine" {