Removed .gz from example command

Running with `.gz`:

```sh
$ ./cayley repl --dbpath=testdata.nt.gz
F0724 00:29:19.795367 10052 load.go:55] Couldn't open file testdata.nt.gz
goroutine 22 [running]:
github.com/barakmich/glog.stacks(0x18cba400, 0x0, 0x0, 0x0)
	/home/barak/src/all-cayley/barakmich-cayley/src/github.com/barakmich/glog/glog.go:810 +0xc7
github.com/barakmich/glog.(*loggingT).output(0x89b5b60, 0x3, 0x18c028c0)
	/home/barak/src/all-cayley/barakmich-cayley/src/github.com/barakmich/glog/glog.go:761 +0x3ad
github.com/barakmich/glog.(*loggingT).println(0x89b5b60, 0x3, 0xf74c6fac, 0x2, 0x2)
	/home/barak/src/all-cayley/barakmich-cayley/src/github.com/barakmich/glog/glog.go:677 +0x9a
github.com/barakmich/glog.Fatalln(0xf74c6fac, 0x2, 0x2)
```