Ensure that imported code with a .css.js file extension isn't treated…

… as CSS

Fixes #31

src/plugin.ts

@@ -21,7 +21,7 @@ export function buildEnd(err?: Error): void {
 }
 
 function useStyleSheetTransform(filename: string) {
-  return filename.match(/\.s?(a|c)ss/);
+  return filename.match(/\.s?(a|c)ss$/);
 }
 
 function useTypescriptTransform(filename: string) {