版本更新下载地址增加后端返回地址，优先取接口返回地址。

KulexiuForStudent/KulexiuForStudent/AppDelegate.m

@@ -256,14 +256,19 @@
                         if ([serviceVersion isEqualToString:storeVersion] || [self isLowerVersionCompareLocalVersion:currentVersion serviceVersion:serviceVersion]) {
                             // desc
                             NSString *descMessage = [[dic ks_dictionaryValueForKey:@"data"] ks_stringValueForKey:@"description"];
+                            NSString *downloadUrl = [[dic ks_dictionaryValueForKey:@"data"] ks_stringValueForKey:@"downloadUrl"];
+                            // 如果没有配置
+                            if ([NSString isEmptyString:downloadUrl]) {
+                                downloadUrl = openUrl;
+                            }
                             // 判断
                             if ([[dic ks_dictionaryValueForKey:@"data"] ks_boolValueForKey:@"isForceUpdate"]) {
                                 self.isNeedUpdate = YES;
-                                [self showAlertWithMemo:storeVersion descMessage:descMessage isforce:YES openUrl:openUrl];
+                                [self showAlertWithMemo:storeVersion descMessage:descMessage isforce:YES openUrl:downloadUrl];
                             }
                             else {
                                 self.isNeedUpdate = NO;
-                                [self showAlertWithMemo:storeVersion descMessage:descMessage isforce:NO openUrl:openUrl];
+                                [self showAlertWithMemo:storeVersion descMessage:descMessage isforce:NO openUrl:downloadUrl];
                             }
                         }