Fix the 'compose' unit test

Author: zsxwing

rxjava-core/src/test/java/rx/ObservableTests.java

@@ -1108,7 +1108,7 @@ public void testCompose() {
         Observable.from(1, 2, 3).compose(new Transformer<Integer, String>() {
 
             @Override
-            public Observable<? extends String> call(Observable<? extends Integer> t1) {
+            public Observable<String> call(Observable<? extends Integer> t1) {
                 return t1.map(new Func1<Integer, String>() {
 
                     @Override