Fix typo "Caffiene" (prometheus#521)

Signed-off-by: Simon Legner <Simon.Legner@gmail.com>

Author: simon04

simpleclient_caffeine/src/main/java/io/prometheus/client/cache/caffeine/CacheMetricsCollector.java

@@ -18,7 +18,7 @@
 
 
 /**
- * Collect metrics from Caffiene's com.github.benmanes.caffeine.cache.Cache.
+ * Collect metrics from Caffeine's com.github.benmanes.caffeine.cache.Cache.
  * <p>
  * <pre>{@code
  *