refactor: standardize quote styles to single quotes across all files

src/svgTransform.js

@@ -1,11 +1,11 @@
 module.exports = {
   process() {
     return {
-      code: `module.exports = {};`,
+      code: 'module.exports = {};',
     };
   },
   getCacheKey() {
     // The output is always the same.
-    return "svgTransform";
+    return 'svgTransform';
   },
 };