chore: simple message changes

lib/engines/puppeteer.js

@@ -141,13 +141,14 @@ class Puppeteer extends engine.Engine {
                 res.send(data);
             } else {
                 // checks if the format is natively supported by puppeteer
-                // and if that's not the case re-encoding is needed
+                // and if that's not the case re-encoding is needed, uses
+                // PNG format as the base one when doing re-encoding
                 const reEncode = ["png", "jpeg", "webp"].indexOf(format) === -1;
-                const type = reEncode ? "png" : format;
+                const baseFormat = reEncode ? "png" : format;
 
                 let data = await page.screenshot({
                     fullPage: fullPage,
-                    type: type
+                    type: baseFormat
                 });
                 if (trim || reEncode) {
                     const image = await jimp.read(data);