Fixed formatting of the ..warning:: block.

Author: osj1961

src/sage/coding/linear_code.py

@@ -2608,9 +2608,9 @@ def minimum_distance(self, algorithm=None):
 
         - Integer, minimum distance of this code
 
-        WARNING::
+        .. WARNING::
 
-        Minimum distance calculation only works for codes over fields of size at most 256.
+            Minimum distance calculation only works for codes over fields of size at most 256.
 
         EXAMPLES::