js: snapshot class incorrectly defining 'exists' as a bool prop, instead of a function

.watchmanconfig

@@ -4,6 +4,7 @@
     "node_modules",
     "android/build",
     "android/.idea",
+    "ios/.idea",
     "android/.gradle",
     "android/gradle",
     ".idea"

lib/modules/database/snapshot.js

@@ -22,7 +22,6 @@ export default class Snapshot {
     this.ref = ref;
     this.key = snapshot.key;
     this.value = snapshot.value;
-    this.exists = snapshot.exists || true;
     this.priority = snapshot.priority === undefined ? null : snapshot.priority;
     this.childKeys = snapshot.childKeys || [];
   }