Change the working directory in the `bin` file

[WilliamMcCumstie]

Now that there is flexec integration, greater care needs to be taken with the working directory. This is because flexec changes the working directory.

Instead, the binary file needs to change it back according to an env var. This line somewhere in the bin/flight-cache file should do the trick:
Dir.chdir(ENV.fetch('FLIGHT_CWD','.'))