Running from a subdirectory results in "Not found a path: spec."

Using git version f2d13f991885ef44e6b54e571e0842222251b111 (on Ubuntu 26.04):

```
$ touch .shellspec
$ mkdir spec
$ shellspec
Running: /bin/sh [sh]


Finished in 0.05 seconds (user: 0.03s, sys: 0.01s) [time: external-time]
0 examples, 0 failures

$ mkdir a
$ cd a
$ shellspec
Not found a path: spec.
$
```