bpo-25810: Clarify eval() docs, it does not keywords (GH-15173)

Author: smokephil

Doc/library/functions.rst

@@ -456,7 +456,7 @@ are always available.  They are listed here in alphabetical order.
               n += 1
 
 
-.. function:: eval(expression, globals=None, locals=None)
+.. function:: eval(expression[, globals[, locals]])
 
    The arguments are a string and optional globals and locals.  If provided,
    *globals* must be a dictionary.  If provided, *locals* can be any mapping