bug #587 try to work with old (2.x?) versions of python

bin/platformio-custom.py

@@ -8,7 +8,7 @@ config.read(prefsLoc)
 version = dict(config.items('VERSION'))
 verStr = "{}.{}.{}".format(version["major"], version["minor"], version["build"])
 
-print(f"Using meshtastic platform-custom.py, firmare version {verStr}")
+print("Using meshtastic platform-custom.py, firmare version " + verStr)
 
 # General options that are passed to the C and C++ compilers
 projenv.Append(CCFLAGS=[