fix(#5): use path.posix.join to get posix style path on windows

Author: dukeluo

lib/utils/filename.js

@@ -16,7 +16,8 @@ const getFilename = (p) => path.posix.basename(p);
  * @type {string} path of folder
  * @param {string} p filename concat with path in posix style
  */
-const getFolderPath = (p) => path.join(path.posix.dirname(p), path.posix.sep);
+const getFolderPath = (p) =>
+  path.posix.join(path.posix.dirname(p), path.posix.sep);
 
 /**
  * @type {string} base name
@@ -49,8 +50,8 @@ const getSubPaths = (p) => {
       if (folder) {
         acc.push(
           index === 0
-            ? path.join(folder, path.posix.sep)
-            : path.join(acc[acc.length - 1], folder, path.posix.sep)
+            ? path.posix.join(folder, path.posix.sep)
+            : path.posix.join(acc[acc.length - 1], folder, path.posix.sep)
         );
       }
       return acc;