Fix number of rotations N as 13 (Resolves TheAlgorithms#12306)

Author: Y-Srivaishnavi

Diff for: ciphers/rot13.py

@@ -1,4 +1,4 @@
-def dencrypt(s: str, n: int = 13) -> str:
+def dencrypt(s: str) -> str:
     """
     https://en.wikipedia.org/wiki/ROT13
 
@@ -9,12 +9,13 @@ def dencrypt(s: str, n: int = 13) -> str:
     >>> dencrypt(s) == msg
     True
     """
+    N = 13
     out = ""
     for c in s:
         if "A" <= c <= "Z":
-            out += chr(ord("A") + (ord(c) - ord("A") + n) % 26)
+            out += chr(ord("A") + (ord(c) - ord("A") + N) % 26)
         elif "a" <= c <= "z":
-            out += chr(ord("a") + (ord(c) - ord("a") + n) % 26)
+            out += chr(ord("a") + (ord(c) - ord("a") + N) % 26)
         else:
             out += c
     return out