rig project sync does not set working directory

[grayside]

All shell executions by a rig project * command should set the working directory to the directory of the config file.

In this way a developer could export the location of a config file in a terminal session, then run commands relevant to the project regardless of their actual working directory.

An example of this can be seen around https://github.com/phase2/rig/blob/develop/cli/commands/project.go#L89.