Ambiguous reference to member (_:quantity:atomically:applicationUsername:simulatesAskToBuyInSandbox:completion:)'

### Platform

- [ X] iOS
- [ ] macOS
- [ ] tvOS

### In app purchase type

- [ ] Consumable
- [X ] Non-consumable
- [ ] Auto-Renewable Subscription
- [ ] Non-Renewing Subscription

### Environment

- [ X] Sandbox
- [ ] Production

### Version
0.13.2

### Related issues
Ambiguous reference to member 'dataTask(with:completionHandler:)' #136

## Report

### Issue summary
Ambiguous reference to member purchaseProduct(_:quantity:atomically:applicationUsername:simulatesAskToBuyInSandbox:completion:)'

### What did you expect to happen
Copied the code given in your documentation

**SwiftyStoreKit.purchaseProduct**(purchase, quantity: 1, atomically: true) { result in
switch result {
case .success(let purchase):
print("Purchase Success: \(purchase.productId)") ... ... ...

### What happened instead

Got compiler error: "Ambiguous reference to member **purchaseProduct**(_:quantity:atomically:applicationUsername:simulatesAskToBuyInSandbox:completion:)'
"

**Is there a work around or fix?**