fixed the step list to avoid linking not yet accessible steps

#90 introduced a glitch when rendering the step list while containing skipped steps.

Consider a flow with 4 steps. Just going from step 1 to 2, the list would be:
1. linked (done)
2. not linked (current step)
3. not linked (skipped)
4. linked

So step 4 is linked mistakenly, which will be fixed by this PR.

/cc @jgornick