docs: updating guidance for conditional class application

[OvidijusParsiunas]

Description of Problem

The guidance for using conditional classes is a little bit misleading as the following:

<div :class="[isActive ? activeClass : '', errorClass]"></div>

'This will always apply errorClass, but will only apply activeClass when isActiveis truthy.'

Can be misinterpreted as:
'This will always apply errorClass, however when isActive is truthy, it will ONLY apply activeClass and nothing else.'

I personally had to take time to test the code myself in order to verify the actual behaviour, which should not be a requirement for documentation readers.

Proposed Solution

I renamed the above to:
'This will always apply errorClass, but activeClass will only be applied when isActive is truthy.'

[NataliaTepluhina]

@OvidijusParsiunas thank you for the rewording! I agree, this sounds a bit more clear 👍🏻