Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Demo/sockets/unicast.py b/Demo/sockets/unicast.py
index 1e9caeb..0a30f35 100644
--- a/Demo/sockets/unicast.py
+++ b/Demo/sockets/unicast.py
@@ -9,7 +9,7 @@
 s.bind(('', 0))
 
 while 1:
-	data = `time.time()` + '\n'
+	data = repr(time.time()) + '\n'
 	s.sendto(data, ('', MYPORT))
 	time.sleep(2)