gzip.open() now needs "rt" instead of just "r"

gzip.open() was causing:

```
  File "/home/stardog/bench_data/freebase/fix_freebase_literal_format.py", line 28, in <module>
    subj, pred, obj, rest = line.split("\t")
                            ~~~~~~~~~~^^^^^^
TypeError: a bytes-like object is required, not 'str'
```

Fix is to change "r" mode to "rt" mode.