Install libunwind8-dev for Ubuntu 14.10

On fresh `14.10` the `make deps` fails with:

```bash
[ 77%] Building CXX object osquery/CMakeFiles/daemon.dir/main/daemon.cpp.o
Linking CXX executable osqueryd
/usr/bin/ld: cannot find -lunwind
collect2: error: ld returned 1 exit status
osquery/CMakeFiles/daemon.dir/build.make:87: recipe for target 'osquery/osqueryd' failed
```