dispose method plopped in the wrong class

It looks to me like you placed the dispose method in BatchProductsRequestDelegate when you intended it to be in InAppPurchase.

I tried out this change in a local phonegap project and get a successful build whereas current master branch causes these errors
```
/Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.m:652:10: error: property 'retainer' not found on object of type
      'BatchProductsRequestDelegate *'
    self.retainer = nil;
         ^
/Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.m:653:10: error: property 'list' not found on object of type
      'BatchProductsRequestDelegate *'
    self.list = nil;
         ^
/Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.m:654:5: error: use of undeclared identifier 'unfinishedTransactions'
    unfinishedTransactions = nil;
    ^
/Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.m:656:62: warning: sending
      'BatchProductsRequestDelegate *const __strong' to parameter of incompatible type 'id<SKPaymentTransactionObserver>'
    [[SKPaymentQueue defaultQueue] removeTransactionObserver:self];
                                                             ^~~~
In file included from /Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.m:9:
In file included from /Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.h:10:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator7.1.sdk/System/Library/Frameworks/StoreKit.fra
mework/Headers/StoreKit.h:11:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator7.1.sdk/System/Library/Frameworks/StoreKit.framework/Headers/SKPayme
ntQueue.h:47:70: note: 
      passing argument to parameter 'observer' here
- (void)removeTransactionObserver:(id <SKPaymentTransactionObserver>)observer __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_0);
                                                                     ^
/Users/aharbick/Sites/boo/platforms/ios/HelloWorld/Plugins/cc.fovea.plugins.inapppurchase/InAppPurchase.m:658:12: error: no visible @interface for 'NSObject' declares the
      selector 'dispose'
    [super dispose];
     ~~~~~ ^~~~~~~
1 warning and 4 errors generated.
```