doc: fix typo in attrs.validators.gt's docstring: ge -> gt (#1423)

Replace operator.ge -> operator.gt, to fix 
a likely copy-paste error.

Author: zed

src/attr/validators.py

@@ -485,7 +485,7 @@ def gt(val):
     A validator that raises `ValueError` if the initializer is called with a
     number smaller or equal to *val*.
 
-    The validator uses `operator.ge` to compare the values.
+    The validator uses `operator.gt` to compare the values.
 
     Args:
        val: Exclusive lower bound for values