Use sys.exit(...) instead of exit(...): exit(...) should not be used in programs

contrib/zmq/zmq_sub.py

@@ -32,7 +32,7 @@ import sys
 
 if not (sys.version_info.major >= 3 and sys.version_info.minor >= 5):
     print("This example only works with Python 3.5 and greater")
-    exit(1)
+    sys.exit(1)
 
 port = 28332
 

contrib/zmq/zmq_sub3.4.py

@@ -36,7 +36,7 @@ import sys
 
 if not (sys.version_info.major >= 3 and sys.version_info.minor >= 4):
     print("This example only works with Python 3.4 and greater")
-    exit(1)
+    sys.exit(1)
 
 port = 28332