Loading profile from `austin>=3.0.0` fails

To reproduce:
1. `conda install austin==3.1`
2. `austin -o outfile.txt python -c "import this"`
3. Upload [outfile.txt](https://github.com/jlfwong/speedscope/files/7379825/austin_3_1.txt) to Speedscope: "Unrecognized format! See documentation about supported formats."

The issue can be "fixed" by using `austin<3.0`, or by using the `austin>=3.0` combined with `austin2speedscope` conversion tool. According to @P403n1x87 since https://github.com/jlfwong/speedscope/pull/336/files was merged the new output format of `austin>=3.0` should be supported. Is this a bug or expected behaviour? Using `austin=2.1.1` with speedscope was always a very seamless experience.

Austin issue for reference: https://github.com/P403n1x87/austin/issues/91