bs-commonjs-generator.js: always use forward slashes in the require path.

Since `path.resolve` is using backslashes on Windows, we ended up with different files. Just replace those with forward slashes.

grunt/bs-commonjs-generator.js

@@ -8,7 +8,7 @@ module.exports = function generateCommonJSModule(grunt, srcFiles, destFilepath)
   var destDir = path.dirname(destFilepath);
 
   function srcPathToDestRequire(srcFilepath) {
-    var requirePath = path.relative(destDir, srcFilepath);
+    var requirePath = path.relative(destDir, srcFilepath).replace(/\\/g, '/');
     return 'require(\'' + requirePath + '\')';
   }