rt: datarate test threshold change

BUG=aomedia:2556

Change-Id: I1182c634760b3cc10f6c909724caebd4a53db6b2
diff --git a/test/datarate_test.cc b/test/datarate_test.cc
index 2f68121..b9a89f4 100644
--- a/test/datarate_test.cc
+++ b/test/datarate_test.cc
@@ -281,7 +281,7 @@
     ASSERT_NO_FATAL_FAILURE(RunLoop(&video));
     ASSERT_GE(effective_datarate_, cfg_.rc_target_bitrate * 0.83)
         << " The datarate for the file is lower than target by too much!";
-    ASSERT_LE(effective_datarate_, cfg_.rc_target_bitrate * 1.17)
+    ASSERT_LE(effective_datarate_, cfg_.rc_target_bitrate * 1.20)
         << " The datarate for the file is greater than target by too much!";
   }
 };