How does Runic Armor and Windspeaker's Blessing stack?

Runic Armor: Increases healing effects by 8% Windspeakers Blessing: Increases heals by 10%

On a self-heal for 10hp, do these masteries increase it like: 10 x (1+0.08) x (1+0.10) = 11.88hp or 10 x (1+0.08+0.10) = 11.80hp

Basically, do the bonuses stack additively or multiplicatively? Is it the same way for the damage increasing masteries?