Enable the no-var rule in the `src/core/fonts_utils.js` file
Enable the no-var rule in the `src/core/fonts_utils.js` file

These changes were made *mostly* automatically, using `gulp lint --fix`, with the following manual changes:

```diff
diff --git a/src/core/fonts_utils.js b/src/core/fonts_utils.js
index f88ce4a8c..c4b3f3808 100644
--- a/src/core/fonts_utils.js
+++ b/src/core/fonts_utils.js
@@ -167,8 +167,8 @@ function type1FontGlyphMapping(properties, builtInEncoding,
glyphNames) {
   }

   // Lastly, merge in the differences.
-  let differences = properties.differences,
-    glyphsUnicodeMap;
+  const differences = properties.differences;
+  let glyphsUnicodeMap;
   if (differences) {
     for (charCode in differences) {
       const glyphName = differences[charCode];
```

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