fix TAROPTS

https://github.com/pytorch/tutorials/pull/758/files#diff-b67911656ef5d18c4ae36cb6741b7965R81 also may need a fix

Author: 9bow

Makefile

@@ -14,7 +14,7 @@ DATADIR       = _data
 GH_PAGES_SOURCES = $(SOURCEDIR) Makefile
 
 ZIPOPTS       ?= -qo
-TAROPTS       ?=
+TAROPTS       ?= -xzf
 
 # Put it first so that "make" without argument is like "make help".
 help: