Deprecation warnings

`tectonic()` and `pdftocairo()` appear to be deprecated. 

When running `test`:
```Julia
┌ Warning: tectonic() is deprecated, use the non-do-block form
│   caller = ip:0x0
└ @ Core :-1
...
┌ Warning: pdftocairo() is deprecated, use the non-do-block form
│   caller = ip:0x0
└ @ Core :-1
```
