Add missing exportVal function to DataSnapshot.

Author: FrankSalad

ios/Firestack/FirestackDatabase.m

@@ -137,6 +137,8 @@ - (NSDictionary *) snapshotToDict:(FIRDataSnapshot *) snapshot
     [dict setValue:snapshot.key forKey:@"key"];
     NSDictionary *val = snapshot.value;
     [dict setObject:val forKey:@"value"];
+    NSDictionary *exportVal = snapshot.valueInExportFormat;
+    [dict setObject:exportVal forKey:@"exportVal"];
     // Snapshot ordering
     NSMutableArray *childKeys = [NSMutableArray array];
     if (snapshot.childrenCount > 0) {

lib/modules/database/snapshot.js

@@ -22,6 +22,7 @@ export default class Snapshot {
     this.ref = ref;
     this.key = snapshot.key;
     this.value = snapshot.value;
+    this.exportVal = snapshot.exportVal;
     this.exists = snapshot.exists || true;
     this.priority = snapshot.priority === undefined ? null : snapshot.priority;
     this.childKeys = snapshot.childKeys || [];
@@ -35,6 +36,10 @@ export default class Snapshot {
     return this.value;
   }
 
+  exportVal() {
+    return this.exportVal;
+  }
+
   child(path: string) {
     const value = deepGet(this.value, path);
     const childRef = this.ref.child(path);