Fixed typo.

Author: akarnokd

src/main/java/rx/internal/operators/OperatorOnBackpressureBlock.java

@@ -24,7 +24,7 @@
 import rx.Subscriber;
 
 /**
- * Operator that uses blocks the producer thread in case a backpressure is needed.
+ * Operator that blocks the producer thread in case a backpressure is needed.
  */
 public class OperatorOnBackpressureBlock<T> implements Operator<T, T> {
     final int max;