doc: Update instance_security_group.md (#775)

Author: remyleone

docs/resources/instance_security_group.md

@@ -119,7 +119,7 @@ The following arguments are supported:
 
 - `project_id` - (Defaults to [provider](../index.md#project_id) `project_id`) The ID of the project the security group is associated with.
 
-- `enable_defaul_security` - Whether to block SMTP on IPv4/IPv6 (Port 25, 465, 587). Set to false will unblock SMTP if your account is authorized to. If your organization is not yet authorized to send SMTP traffic, [open a support ticket](https://console.scaleway.com/support/tickets).
+- `enable_default_security` - Whether to block SMTP on IPv4/IPv6 (Port 25, 465, 587). Set to false will unblock SMTP if your account is authorized to. If your organization is not yet authorized to send SMTP traffic, [open a support ticket](https://console.scaleway.com/support/tickets).
 
 The `inbound_rule` and `outbound_rule` block supports: