remove .py from naval fate example
diff --git a/examples/naval_fate.go b/examples/naval_fate.go
index ef34bc4..8fa4604 100644
--- a/examples/naval_fate.go
+++ b/examples/naval_fate.go
@@ -9,12 +9,12 @@
 	usage := `Naval Fate.
 
 Usage:
-  naval_fate.py ship new <name>...
-  naval_fate.py ship <name> move <x> <y> [--speed=<kn>]
-  naval_fate.py ship shoot <x> <y>
-  naval_fate.py mine (set|remove) <x> <y> [--moored|--drifting]
-  naval_fate.py -h | --help
-  naval_fate.py --version
+  naval_fate ship new <name>...
+  naval_fate ship <name> move <x> <y> [--speed=<kn>]
+  naval_fate ship shoot <x> <y>
+  naval_fate mine (set|remove) <x> <y> [--moored|--drifting]
+  naval_fate -h | --help
+  naval_fate --version
 
 Options:
   -h --help     Show this screen.