fix: sources in source maps have relative paths (#1219)

Author: isaacl

src/utils.js

@@ -484,7 +484,7 @@ function normalizeSourceMapForRuntime(map, loaderContext) {
         path.relative(loaderContext.rootContext, absoluteSource)
       );
 
-      return `webpack://${contextifyPath}`;
+      return `webpack://./${contextifyPath}`;
     });
   }