fix(monster): add missing legendary resistance (#482)

Forn ancient blue dragon.

Author: Rarst

src/5e-SRD-Monsters.json

@@ -3452,6 +3452,16 @@
     "languages": "Common, Draconic",
     "challenge_rating": 23,
     "xp": 50000,
+    "special_abilities": [
+      {
+        "name": "Legendary Resistance",
+        "desc": "If the dragon fails a saving throw, it can choose to succeed instead.",
+        "usage": {
+          "type": "per day",
+          "times": 3
+        }
+      }
+    ],
     "actions": [
       {
         "name": "Multiattack",