Issue #5067: improve some json error messages.
Patch by Serhiy Storchaka.
diff --git a/Lib/json/tool.py b/Lib/json/tool.py
index c37bb77..b2c786d 100644
--- a/Lib/json/tool.py
+++ b/Lib/json/tool.py
@@ -7,7 +7,7 @@
         "json": "obj"
     }
     $ echo '{ 1.2:3.4}' | python -m json.tool
-    Expecting property name: line 1 column 2 (char 2)
+    Expecting property name enclosed in double quotes: line 1 column 2 (char 2)
 
 """
 import sys