Changed Python version in Debian/Ubuntu install instructions (espressif#1043)

As discussed in espressif#1042.

Author: birgersp

docs/arduino-ide/debian_ubuntu.md

@@ -16,7 +16,7 @@ Installation instructions for Debian / Ubuntu OS
   cd esp32 && \
   git submodule update --init --recursive && \
   cd tools && \
-  python get.py
+  python2 get.py
   ```
 - Restart Arduino IDE
 
@@ -32,4 +32,4 @@ Installation instructions for Debian / Ubuntu OS
   cd esp32 && \
   git submodule update --init --recursive && \
   cd tools && \
-  python get.py```
+  python2 get.py```