[egs] mini_librispeech: allow relative pathnames in download_and_untar.sh (#2689)

Author: desh2608

egs/mini_librispeech/s5/local/download_and_untar.sh

@@ -77,6 +77,7 @@ if [ ! -f $data/$part.tar.gz ]; then
     echo "$0: error executing wget $full_url"
     exit 1;
   fi
+  cd -
 fi
 
 cd $data