bpo-18610: Update wsgiref.validate docstring for wsgi.input read() (pythonGH-11663)

Author: csabella

Lib/wsgiref/validate.py

@@ -77,7 +77,7 @@
 
 * That wsgi.input is used properly:
 
-  - .read() is called with zero or one argument
+  - .read() is called with exactly one argument
 
   - That it returns a string