Can't import nested modules

I created a file `./lib/data/list.lc` and tried to import it, got the following errors:
```
> :m + data.list
lambda-calculus: ./lib/data.lc: openFile: does not exist (No such file or directory)

> :m + data/list
lambda-calculus: ./lib/data.lc: openFile: does not exist (No such file or directory)
```