http模块添加expectString方法，避免返回字符串时反序列化报错

magic-api/src/main/java/org/ssssssss/magicapi/modules/http/HttpModule.java

@@ -133,6 +133,12 @@ public class HttpModule {
 		return this;
 	}
 
+	@Comment("设置返回值为`String`")
+	public HttpModule expectString() {
+		this.responseType = String.class;
+		return this;
+	}
+
 	@Comment("发送`POST`请求")
 	public ResponseEntity<?> post() {
 		this.method(HttpMethod.POST);