Explicitly fetch [email protected] from github

airrohr-firmware/platformio.ini

@@ -88,7 +88,7 @@ extra_scripts = platformio_script.py
 # When the requirement for Arduino Core is raised, this
 # needs to be adjusted to the matching version from
 # https://github.com/platformio/platform-espressif8266/releases
-platform_version = espressif8266@3.1.0
+platform_version = git+https://github.com/platformio/platform-espressif8266#v3.1.0
 platform_version_esp32 = [email protected] ; using Arduino core 1.0.4
 
 [DISABLEDenv:lolin_d32_pro_debug]