fix HR zones assignment

[miacono]

HR measures were wrongly assigned to the previous zone.

Before
zone 1 was less than 50%
zone 2 went from 50% to 60%
and so on.

That's wrong because zone 1 goes from 50% to 60%, etc.
I changed this considering HR less than 50% as belonging to zone 1.

New behaviour
zone 1 is less than 60%
zone 2 goes from 60% to 70%
zone 3 goes from 70% to 80%
zone 4 goes from 80% to 90%
zone 5 is greater than 90%

This works fine in my environment.