Set class file version in VerticalClassMerger

Change-Id: I5e282ba9169705efac3b3fa7d03abcd695e7e668
diff --git a/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java b/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java
index a8fd776..637f763 100644
--- a/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java
+++ b/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java
@@ -699,7 +699,8 @@
           ParameterAnnotationsList.empty(),
           new SynthesizedCode(
               new ForwardMethodSourceCode(holder, proto, holder, invocationTarget, Type.DIRECT),
-              registry -> registry.registerInvokeDirect(invocationTarget)));
+              registry -> registry.registerInvokeDirect(invocationTarget)),
+          signature.hasClassFileVersion() ? signature.getClassFileVersion() : -1);
     }
 
     // Returns the method that shadows the given method, or null if method is not shadowed.