redis_firewall_rule: simplify regex in firewall rule name (#2911)

This PR simplifies the regex in redis firewall rule name (original merged pr is #2906 )

azurerm/resource_arm_redis_firewall_rule.go

@@ -161,7 +161,7 @@ func resourceArmRedisFirewallRuleDelete(d *schema.ResourceData, meta interface{}
 func validateRedisFirewallRuleName(v interface{}, k string) (warnings []string, errors []error) {
 	value := v.(string)
 
-	if matched := regexp.MustCompile(`^[0-9a-zA-Z_]+$`).Match([]byte(value)); !matched {
+	if matched := regexp.MustCompile(`^\w+$`).Match([]byte(value)); !matched {
 		errors = append(errors, fmt.Errorf("%q may only contain alphanumeric characters and underscores", k))
 	}