fix: hardcoded '/' in normalized options.fs, fixes #412, #408

Changes including:
- will not call fs.resolve when normalizing `fs`
- removed hardcoded `/`
- mandatory `fs.dirname` for relative reference
- mandatory `fs.sep`, defaults to '/'

src/liquid-options.ts

@@ -169,5 +169,5 @@ export function normalizeDirectoryList (value: any): string[] {
   let list: string[] = []
   if (_.isArray(value)) list = value
   if (_.isString(value)) list = [value]
-  return list.map(str => fs.resolve(str, '.', '')).map(str => str[str.length - 1] !== '/' ? str + '/' : str)
+  return list
 }