convert shebang lines: python -> python3
diff --git a/Demo/sockets/echosvr.py b/Demo/sockets/echosvr.py
index 7de6391..6f7030e 100755
--- a/Demo/sockets/echosvr.py
+++ b/Demo/sockets/echosvr.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # Python implementation of an 'echo' tcp server: echo all data it receives.
 #