Step on b-numberinput is not updated when prop changes

[rcoundon]

Buefy version: 0.8.20
Vuejs version: 2.6.11
OS/Browser: Mac Catalina/Chrome

Description

As per Discord:
When the step prop value changes this is not reflected in increment and decrement

I've created a simple illustration, in the 2nd input box I'm providing the ability to update the step by tying it to the "step" data property via v-model.
In the b-numberinput I have :step="step"
It works on initial load but doesn't change the step when I update it.
https://codepen.io/rcoundon/pen/ZEQPRRQ

Expected behavior

The new step value allows for a new step when clicking increment/decrement

Actual behavior

The step stays the same

I've nearly got a PR ready to fix this.