docs: Correct which attribute RuleBasedSampler checks

[t2t2]

reference:

splunk-otel-java/custom/src/main/java/com/splunk/opentelemetry/sampler/RuleBasedSamplerProvider.java

Lines 54 to 56 in 349326b

	private AttributeKey<String> getHttpPathAttribute() {
	return UrlAttributes.URL_PATH;
	}

[robsunday]

Nice catch