statetree fix

Hi,

I found an error in the statetree plugin.

in StateTreeTypes.h:440

The random variance accessor actually return the Duration. Look like a copy paste issue.

In 5.4.2 we have:

/** @return the maximum random variance. */
float GetRandomVariance() const
{
return Duration / Scale;
}

Should be

/** @return the maximum random variance. */
float GetRandomVariance() const
{
	return RandomVariance / Scale;
}