Fix stream_insert_context docstring

This was never updated when timestamps were changed from floats to
ints.

nilmdb/client/client.py

@@ -145,8 +145,8 @@ class Client():
 
         Example:
           with client.stream_insert_context('/path', start, end) as ctx:
-            ctx.insert('1234567890.0 1 2 3 4\\n')
-            ctx.insert('1234567891.0 1 2 3 4\\n')
+            ctx.insert('1234567890000000 1 2 3 4\\n')
+            ctx.insert('1234567891000000 1 2 3 4\\n')
 
         For more details, see help for nilmdb.client.client.StreamInserter