[DOCS] EXCLUDE logical wording: "not all" should be "none"

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.6/static/sql-createtable.html
Description:

The EXCLUDE docs say 

"The EXCLUDE clause defines an exclusion constraint, which guarantees that
if any two rows are compared on the specified column(s) or expression(s)
using the specified operator(s), not all of these comparisons will return
TRUE."

It also says "for equality, this is equivalent to a UNIQUE constraint".

The current documentation saying "not all" is not the same as a unique
constraint, because in the case of equality, it is logically stating that
"All rows - 1 can be equal", which satisfies "not all" pairs. Instead it
should say that no pairs, or none, return true.