Fix directory check in extract function

The directory check is not robust and fails if the path uses the Windows style path separator and not the unix style. A function "is_dir" already exists and accounts for this so this change switches to using that function instead.

src/read.rs

@@ -456,7 +456,7 @@ impl<R: Read + io::Seek> ZipArchive<R> {
 
             let outpath = directory.as_ref().join(filepath);
 
-            if file.name().ends_with('/') {
+            if file.is_dir() {
                 fs::create_dir_all(&outpath)?;
             } else {
                 if let Some(p) = outpath.parent() {