fix(typings): fixed type of getCountryCode() to return number not string

fix #39

index.d.ts

@@ -35,7 +35,7 @@ declare namespace AwesomePhonenumber
 		getNumber( type?: PhoneNumberFormat ): string;
 		getNumberFrom( regionCode: string ): string;
 		getRegionCode( ): string;
-		getCountryCode( ): string;
+		getCountryCode( ): number;
 		toJSON( ): any;
 
 		static getCountryCodeForRegionCode( regionCode: string ): number;