plugin/erratic: apply default truncate amount of 2 for bare truncate (#8240)

plugin/erratic/setup.go

@@ -86,6 +86,8 @@ func parseErratic(c *caddy.Controller) (*Erratic, error) {
 					return nil, c.ArgErr()
 				}
 
+				// Defaults.
+				e.truncate = 2
 				if len(args) == 0 {
 					continue
 				}

plugin/erratic/setup_test.go

@@ -51,6 +51,10 @@ func TestParseErratic(t *testing.T) {
 			drop 3
 			delay
 		}`, false, 3, 2, 0},
+		{`erratic {
+			drop 3
+			truncate
+		}`, false, 3, 0, 2},
 		// fails
 		{`erratic {
 			drop -1