Add go to definition support for dot sourced file paths

[kaylaerdmann]

When peek definition or go to definition are used on a dot sourced file nothing happens. This is currently the same behavior that happens on built-in commands where the source file can't be found.

Should peek and go to definition bring the user to the very beginning of the dot sourced file when those features are used?

[daviwil]

This is definitely a good idea, will add it for 0.2.