Fixed a minor errors

Author: Taritsyn

src/JavaScriptEngineSwitcher.ChakraCore/JsRt/JsContext.cs

@@ -438,7 +438,7 @@ public static byte[] SerializeScript(string script)
 			if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
 			{
 				buffer = null;
-				ulong bufferSize = 0;
+				uint bufferSize = 0;
 
 				errorCode = NativeMethods.JsSerializeScript(script, buffer, ref bufferSize);
 				JsErrorHelpers.ThrowIfError(errorCode);

src/JavaScriptEngineSwitcher.ChakraCore/JsRt/NativeMethods.cs

@@ -375,7 +375,7 @@ internal static extern JsErrorCode JsRunScript(string script, JsSourceContext so
 			string sourceUrl, out JsValue result);
 
 		[DllImport(DllName.Universal, CharSet = CharSet.Unicode)]
-		internal static extern JsErrorCode JsSerializeScript(string script, byte[] buffer, ref ulong bufferSize);
+		internal static extern JsErrorCode JsSerializeScript(string script, byte[] buffer, ref uint bufferSize);
 
 		[DllImport(DllName.Universal)]
 		internal static extern JsErrorCode JsParseSerializedScriptWithCallback(