Update Unoconv submodule

Includes changes to unconv over last 7 months. See unoconv issues 134, 140, 159 and 170 for details of what's changed there.

There has been an alteration to how unoconv processes the output argument. Previously, it was possible to state ``--output="file_to_output_to.ext"`` and as long as this didn't already exist as a folder, unoconv would create it as a file and output to it. The new behaviour is to create it literally as a folder, and place the converted output within it, appending the appropriate extension to the new file:
```shell
# command:
unoconv --output="./output_file.new" --format=new "./input_file.old"
# old behaviour:
./output_file.new
# new behaviour:
./output_file.new/input_file.new
```

Needless to say, this breaks both eyeVisor and eyeDocs, so this pull request includes a quick, if inelegant, fix for both. eyePresentation is unaffected, interestingly enough, as it already expects a folder to be created containing the file(s) it needs.