Hard coded path for mediainfo

There's a hard coded path to `/usr/local/bin/mediainfo` in `autodetect_file.c`:

https://github.com/Comcast/caption-inspector/blob/476326f08a43ce38ecd1ea58b8910d7015e80cac/src/utils/autodetect_file.c#L52

As a result, if you have installed `mediainfo` in another directory that is in the `PATH` (eg: `/usr/bin`), such as installing it via `apt install mediainfo`, `caption-inspector` won't find it.

The Docker build appears to work around this by moving the binary:

https://github.com/Comcast/caption-inspector/blob/476326f08a43ce38ecd1ea58b8910d7015e80cac/Dockerfile#L62

The easy fix is to change this to:

```c
char* mediaInfoInvokeStr = "mediainfo";
```

But it may also need a fix-up for the Docker container which puts the binary elsewhere.