docs: fix valuesByTTL() noTTL description

Correctly state that noTTL contains items where expiry === 0, regardless of cache ttl setting

Author: avoidwork

docs/API.md

@@ -639,7 +639,7 @@ console.log(cache.valuesByTTL());
 **Returns:** `Object` - Object with three properties:
 - `valid` - Array of valid (non-expired) values
 - `expired` - Array of expired values
-- `noTTL` - Array of values without TTL (when `ttl=0`)
+- `noTTL` - Array of values without TTL (`expiry === 0`, regardless of cache `ttl` setting)
 
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