Fix minor typo

Author: stewartadcock

gpiozero/cli/pinout.py

@@ -56,7 +56,7 @@ def main():
         try:
             pi_info().pprint(color=args.color)
         except IOError:
-            print('This device is not an Raspberry Pi?')
+            print('This device is not a Raspberry Pi?')
             exit(2)
     else:
         pi_info(args.revision).pprint(color=args.color)