Use dist path for library JSON files of GUI

In conjunction with scratchfoundation/scratch-gui#5277, since we removed /src from the published gui files

Author: paulkaplan

scripts/lib/libraries.js

@@ -1,7 +1,7 @@
-const backdrops = require('scratch-gui/src/lib/libraries/backdrops.json');
-const costumes = require('scratch-gui/src/lib/libraries/costumes.json');
-const sounds = require('scratch-gui/src/lib/libraries/sounds.json');
-const sprites = require('scratch-gui/src/lib/libraries/sprites.json');
+const backdrops = require('scratch-gui/dist/libraries/backdrops.json');
+const costumes = require('scratch-gui/dist/libraries/costumes.json');
+const sounds = require('scratch-gui/dist/libraries/sounds.json');
+const sprites = require('scratch-gui/dist/libraries/sprites.json');
 
 const libraries = {
     backdrops,