Convert X509ExtTests to use pytest-style tests (#564)

diff --git a/examples/simple/server.py b/examples/simple/server.py
index 19f6d21..9cce9e0 100644
--- a/examples/simple/server.py
+++ b/examples/simple/server.py
@@ -67,6 +67,7 @@
         cli.shutdown()
     cli.close()
 
+
 while 1:
     try:
         r, w, _ = select.select(