Enabling micro run for subfolders

[crufter]

To reproduce the issue:

• Step into micro/services repo locally.
• Issue micro run account/api.

You will see:

$ micro run account/api
go: cannot find main module, but found .git/config in /home/crufter/code/src/github.com/micro/services
	to create a module there, run:
	go mod init

This is because micro run issues go run in the current folder (ie. micro/services) rather than in the subfolder. This PR fixes that by setting the Dir property for cmds executed.

Context: The reason I needed to do micro run [subfolder] is so micro run correctly sets the name of the service.