Update lib/converter.js

lib/converter.js

@@ -10,7 +10,7 @@ async function convertWebpToPng(input) {
          const converting = await sharp(images);
          const converted = converting.toFormat('png').png({ quality: 90 }).toBuffer();
          resolve(converted);
-      } else {
+      } else if(typeof input == "object") {
          const converting = await sharp(input);
          const converted = converting.toFormat('png').png({ quality: 90 }).toBuffer();
          resolve(converted);