Fixes in .drone.yml: Python3, platformio instead of pio.

.drone.yml

@@ -3,8 +3,8 @@ name: default
 
 steps:
   - name: Full
-    image: python:2.7
+    image: python:3
     commands:
-      - pip install pio
+      - pip install -U platformio
       - cp include/config.sample.h include/config.h
       - pio run -DCONFIG_USABLE