Fix r8lib.jar retrieval in retrace.py

Change-Id: I77afb565b125bc985f84c4cdef704c9ec14bdcff
diff --git a/tools/retrace.py b/tools/retrace.py
index 911c646..9768ff3 100755
--- a/tools/retrace.py
+++ b/tools/retrace.py
@@ -188,7 +188,7 @@
         )
 
     if not r8jar:
-        r8jar = utils.R8_JAR if no_r8lib else utils.R8LIB
+        r8jar = utils.R8_JAR if no_r8lib else utils.R8LIB_JAR
 
     retrace_args += [
         '-cp', r8jar, 'com.android.tools.r8.retrace.Retrace', map_path