fix several typos

Author: Steven Wu

src/test/java/rx/internal/operators/OperatorOnBackpressureBufferTest.java

@@ -93,7 +93,7 @@ public void testFixBackpressureBufferNegativeCapacity() throws InterruptedExcept
 
     @Test(expected = IllegalArgumentException.class)
     public void testFixBackpressureBufferZeroCapacity() throws InterruptedException {
-        Observable.empty().onBackpressureBuffer(-1);
+        Observable.empty().onBackpressureBuffer(0);
     }
 
     @Test

src/test/java/rx/internal/operators/OperatorOnBackpressureDropTest.java

@@ -46,7 +46,7 @@ public void testNoBackpressureSupport() {
     @Test(timeout = 500)
     public void testWithObserveOn() throws InterruptedException {
         TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
-        Observable.range(0, RxRingBuffer.SIZE * 10).onBackpressureDrop().onBackpressureDrop().observeOn(Schedulers.io()).subscribe(ts);
+        Observable.range(0, RxRingBuffer.SIZE * 10).onBackpressureDrop().observeOn(Schedulers.io()).subscribe(ts);
         ts.awaitTerminalEvent();
     }