Fix schematic diagram URL

It's no longer alpha, apparently.

Author: laanwj

docs/devices/open-source-hardware/esp32-series/lora-32/wifi-lora-32/wifi-lora-32-v4/wifi-lora-32-v4.md

@@ -50,7 +50,7 @@ The classic WiFi LoRa 32 development board has been upgraded to the all-new V4 v
 
 ## Important Resources
 - [Datasheet](https://resource.heltec.cn/download/WiFi_LoRa_32_V4/datasheet/WiFi_LoRa_32_V4.2.0.pdf)
-- [Schematic diagram](https://resource.heltec.cn/download/WiFi_LoRa_32_V4/Schematic/WiFi_LoRa_32_V4.1_alpha.pdf)
+- [Schematic diagram](https://resource.heltec.cn/download/WiFi_LoRa_32_V4/Schematic/WiFi_LoRa_32_V4.2.pdf)
 - [Pin Map](https://resource.heltec.cn/download/WiFi_LoRa_32_V4/Pinmap/V4_pinmap.png)
 - [Related links](https://resource.heltec.cn/download/WiFi_LoRa_32_V4)
 
@@ -60,4 +60,4 @@ The classic WiFi LoRa 32 development board has been upgraded to the all-new V4 v
 - [Install development environment](/docs/devices/open-source-hardware/esp32-series/esp32-quick-start)
 - [Applied to LoRaWAN](/docs/devices/open-source-hardware/esp32-series/esp32-quick-start?esp32=lorawan)
 - [Applied to Meshtatic](/docs/devices/open-source-hardware/esp32-series/esp32-quick-start?esp32=meshtastic)
-- [How to use license](/docs/devices/general-docs/how_to_use_license)
+- [How to use license](/docs/devices/general-docs/how_to_use_license)