[split] Fix arg type in RetryingFilter.apply

`RetryingFilter.apply` should let its `shouldRetry` argument take a
`Try[Nothing]` instead of a `Try[Rep]`, since it's immediately turned
into a `RetryPolicy[Try[Nothing]]`.

Github-pull-request: twitter#108
Signed-off-by: Steve Gury <[email protected]>

RB_ID=86676

Author: jdanbrown

finagle-core/src/main/scala/com/twitter/finagle/service/RetryingFilter.scala

@@ -125,7 +125,7 @@ object RetryingFilter {
   def apply[Req, Rep](
     backoffs: Stream[Duration],
     statsReceiver: StatsReceiver = NullStatsReceiver
-  )(shouldRetry: PartialFunction[Try[Rep], Boolean])(implicit timer: Timer) =
+  )(shouldRetry: PartialFunction[Try[Nothing], Boolean])(implicit timer: Timer) =
     new RetryingFilter[Req, Rep](RetryPolicy.backoff(backoffs)(shouldRetry), timer, statsReceiver)
 }