Update src/sage/sets/primes.py

Co-authored-by: Martin Rubey <axiomize@yahoo.de>

Author: xcaruso

src/sage/sets/primes.py

@@ -559,7 +559,7 @@ def in_range(self, start, stop=None):
             sage: P.in_range(50, 100)
             [61, 67, 73, 79, 97]
 
-        When a unique integer is passed, it is interpreted as the
+        When a single integer is passed, it is interpreted as the
         upper bound::
 
             sage: P.in_range(50)