fix: slow performance on derivationKey method. Closes #3

ios/RCTPBKDF2/RCTPBKDF2.m

@@ -5,7 +5,7 @@
 
 RCT_EXPORT_MODULE()
 
-RCT_EXPORT_METHOD(derivationKey:(NSString *)password salt:(NSString *)salt iterations:(nonnull NSNumber *)iterations
+RCT_EXPORT_METHOD(derivationKey:(NSString *)password salt:(NSString *)salt iterations:(nonnull int *)iterations
                   resolver:(RCTPromiseResolveBlock)resolve
                   rejecter:(RCTPromiseRejectBlock)reject) {
     NSError *error = nil;

ios/RCTPBKDF2/lib/PBKDF2.h

@@ -1,6 +1,6 @@
 #import <Foundation/Foundation.h>
 
 @interface PBKDF2 : NSObject
-+ (NSString *) derivationKey:(NSString *)password salt: (NSString *)salt iterations: (nonnull NSNumber *)iterations;
++ (NSString *) derivationKey:(NSString *)password salt: (NSString *)salt iterations: (nonnull int *)iterations;
 + (NSString *) toHex: (NSData *)nsdata;
 @end

ios/RCTPBKDF2/lib/PBKDF2.m

@@ -13,7 +13,7 @@
     return hexStr;
 }
 
-+ (NSString *) derivationKey:(NSString *)password salt: (NSString *)salt iterations: (nonnull NSNumber *)iterations {
++ (NSString *) derivationKey:(NSString *)password salt: (NSString *)salt iterations: (nonnull int *)iterations {
     // Data of String to generate Hash key(hexa decimal string).
     NSData *passwordData = [password dataUsingEncoding:NSUTF8StringEncoding];
     NSData *saltData = [salt dataUsingEncoding:NSUTF8StringEncoding];