Added fullstackreact#171

and my NSString *clientID fix, which might not be as good as
https://github.com/fullstackreact/react-native-oauth/blob/2f8c8d1483526bbc8a6ca72183c6d11a71538ad3/ios/OAuthManager/OAuthManager.m

Author: SailingSteve

ios/OAuthManager/OAuthManager.m

@@ -303,8 +303,7 @@ - (NSDictionary *) getConfigForProvider:(NSString *)name
     NSMutableDictionary *cfg = [[manager getConfigForProvider:providerName] mutableCopy];
 
     DCTAuthAccount *existingAccount = [manager accountForProvider:providerName];
-    NSString *clientID = ((DCTOAuth2Credential *) existingAccount).clientID;
-        NSString *clientID = ([providerName isEqualToString:@"google"]) ? ((DCTOAuth2Credential *) existingAccount).clientID : (NSString *)nil;
+    NSString *clientID = ([providerName isEqualToString:@"google"]) ? ((DCTOAuth2Credential *) existingAccount).clientID : (NSString *)nil;
 
     if (([providerName isEqualToString:@"google"] && existingAccount && clientID != nil)
         || (![providerName isEqualToString:@"google"] && existingAccount != nil)) {