use correct instance of valueOrDefault in FormattingRule

[Mauin]

Similar to #1152 I think this rule should use the ConfigAware#valueOrDefault method instead of accessing the config directly.

[arturbosch]

This change is actually wrong, the android property should be declared once for the ruleSet:

	/**
	 * Wrapped configuration of the ruleSet this rule is in.
	 */
	val config: Config

Just using valueOrDefault will return the subConfig of this rule while config.valueOrDefault returns properties from the ruleSet itself.
Jap, as you mentioned in #1153 and #1152 maybe we should rename config to ruleSetConfig?

[Mauin]

Ah, I see. Thanks @arturbosch! I just checked all accessors of the config property directly and this was the only usage in the rules.