Update the signature of lift

Author: zsxwing

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/JavaConversions.scala

@@ -55,7 +55,7 @@ object JavaConversions {
     }
   }
 
-  implicit def toJavaOperator[T, R](operator: Subscriber[R] => Subscriber[_ >: T]): rx.Observable.Operator[R, T] = {
+  implicit def toJavaOperator[T, R](operator: Subscriber[R] => Subscriber[T]): rx.Observable.Operator[R, T] = {
     new rx.Observable.Operator[R, T] {
       override def call(subscriber: rx.Subscriber[_ >: R]): rx.Subscriber[_ >: T] = {
         toJavaSubscriber[T](operator(toScalaSubscriber[R](subscriber)))

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/Observable.scala

@@ -2572,7 +2572,7 @@ trait Observable[+T]
    * @return an Observable that emits values that are the result of applying the bind function to the values
    *         of the current Observable
    */
-  def lift[R](operator: Subscriber[R] => Subscriber[_ >: T]): Observable[R] = {
+  def lift[R](operator: Subscriber[R] => Subscriber[T]): Observable[R] = {
     toScalaObservable(asJavaObservable.lift(toJavaOperator[T, R](operator)))
   }
 }

language-adaptors/rxjava-scala/src/test/scala/rx/lang/scala/CompletenessTest.scala

@@ -79,7 +79,7 @@ class CompletenessTest extends JUnitSuite {
       "firstOrDefault(T)" -> "firstOrElse(=> U)",
       "firstOrDefault(Func1[_ >: T, Boolean], T)" -> "[use `.filter(condition).firstOrElse(default)`]",
       "groupBy(Func1[_ >: T, _ <: K], Func1[_ >: T, _ <: R])" -> "[use `groupBy` and `map`]",
-      "lift(Operator[_ <: R, _ >: T])" -> "lift(Subscriber[R] => Subscriber[_ >: T])",
+      "lift(Operator[_ <: R, _ >: T])" -> "lift(Subscriber[R] => Subscriber[T])",
       "mapMany(Func1[_ >: T, _ <: Observable[_ <: R]])" -> "flatMap(T => Observable[R])",
       "mapWithIndex(Func2[_ >: T, Integer, _ <: R])" -> "[combine `zipWithIndex` with `map` or with a for comprehension]",
       "onErrorResumeNext(Func1[Throwable, _ <: Observable[_ <: T]])" -> "onErrorResumeNext(Throwable => Observable[U])",