Enable the `no-var` linting rule in `src/core/image.js`
Enable the `no-var` linting rule in `src/core/image.js`

This is done automatically with `gulp lint --fix` and the following
manual changes:

```diff
diff --git a/src/core/image.js b/src/core/image.js
index 35c06b8ab..e718b9937 100644
--- a/src/core/image.js
+++ b/src/core/image.js
@@ -97,7 +97,7 @@ class PDFImage {
     if (isName(filter)) {
       switch (filter.name) {
         case "JPXDecode":
-          var jpxImage = new JpxImage();
+          const jpxImage = new JpxImage();
           jpxImage.parseImageProperties(image.stream);
           image.stream.reset();
```

showpad/mozilla-pdf.js,mozilla/pdf.js,mozilla/pdf.js,xavier114fch/pdf.js,timvandermeij/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,xavier114fch/pdf.js,nawawi/pdf.js,macroplant/pdf.js,macroplant/pdf.js,timvandermeij/pdf.js,timvandermeij/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,Shoobx/pdf.js,Snuffleupagus/pdf.js,Shoobx/pdf.js,Snuffleupagus/pdf.js