Check interactive mode instead of login shell

[soraxas]

Related to #12 where pyenv is not being initialized with this plugin.

The current conf.d script checks whether it is login shell or not, if so it will then set the PATH variable.

However, it never triggers in my system (I am using Arch) as I think because the fish shell is never used to Start X, even though fish is my default shell. Therefore, line 16-17 never ended up running. This is related to this comment

I have changed the checking from checking if it's login-shell to checking if it's interactive shell, and it fixes the problem.

[ovv]

:+1: can we merge that ?