Don't use deprecated Throwables.propagateIfInstanceOf

Replace with Throwables.throwIfInstanceOf.

Change-Id: I56b6d5aebdd4ef6bba3fe431d553b6c2b7a3ca3c

gitiles-servlet/src/main/java/com/google/gitiles/TimeCache.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/TimeCache.java b/gitiles-servlet/src/main/java/com/google/gitiles/TimeCache.java
index 4159517..a019d0f 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/TimeCache.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/TimeCache.java
@@ -74,7 +74,7 @@
             return Long.MIN_VALUE;
           });
     } catch (ExecutionException e) {
-      Throwables.propagateIfInstanceOf(e.getCause(), IOException.class);
+      Throwables.throwIfInstanceOf(e.getCause(), IOException.class);
       throw new IOException(e);
     }
   }