Update bond_constraints.py

This modifies slightly default constraints for some charged atoms. Thereby we follow the updated constraints of RDKit. This fixes issue #127

selfies/bond_constraints.py

@@ -9,9 +9,9 @@
     "B": 3, "B+1": 2, "B-1": 4,
     "O": 2, "O+1": 3, "O-1": 1,
     "N": 3, "N+1": 4, "N-1": 2,
-    "C": 4, "C+1": 5, "C-1": 3,
-    "P": 5, "P+1": 6, "P-1": 4,
-    "S": 6, "S+1": 7, "S-1": 5,
+    "C": 4, "C+1": 3, "C-1": 3,
+    "P": 5, "P+1": 4, "P-1": 6,
+    "S": 6, "S+1": 5, "S-1": 5,
     "?": 8
 }
 
@@ -48,7 +48,7 @@ def get_preset_constraints(name: str) -> Dict[str, int]:
         +-----------------+-----------+---+---+-----+-----+---+-----+-----+
         |                 | Cl, Br, I | N | P | P+1 | P-1 | S | S+1 | S-1 |
         +-----------------+-----------+---+---+-----+-----+---+-----+-----+
-        | ``default``     |     1     | 3 | 5 |  6  |  4  | 6 |  7  |  5  |
+        | ``default``     |     1     | 3 | 5 |  4  |  6  | 6 |  5  |  5  |
         +-----------------+-----------+---+---+-----+-----+---+-----+-----+
         | ``octet_rule``  |     1     | 3 | 3 |  4  |  2  | 2 |  3  |  1  |
         +-----------------+-----------+---+---+-----+-----+---+-----+-----+