Fix the problem that the compilation fails when the compilation parameter is --no-default-features.

Update mod.rs

src/types/external/mod.rs

@@ -7,10 +7,11 @@ mod integers;
 mod list;
 mod optional;
 mod string;
-mod url;
 mod uuid;
 
 #[cfg(feature = "bson")]
 mod bson;
 #[cfg(feature = "chrono_tz")]
 mod chrono_tz;
+#[cfg(feature = "url")]
+mod url;