Fix connection_name parameter sql_database_instacne docs

connection_name is a read only parameter that was added in hashicorp#406.

website/docs/r/sql_database_instance.html.markdown

@@ -68,8 +68,6 @@ The following arguments are supported:
 
 - - -
 
-* `connection_name` - (Optional) The connection name of the instance to be used in connection strings.
-
 * `database_version` - (Optional, Default: `MYSQL_5_6`) The MySQL version to
     use. Can be `MYSQL_5_6`, `MYSQL_5_7` or `POSTGRES_9_6` for second-generation
     instances, or `MYSQL_5_5` or `MYSQL_5_6` for first-generation instances.
@@ -244,6 +242,7 @@ when the resource is configured with a `count`.
 
 * `server_ca_cert.0.sha1_fingerprint` - SHA Fingerprint of the CA Cert.
 
+* `connection_name` - The connection name of the instance to be used in connection strings.
 
 ## Timeouts