Lower BasicRateTargetingVBR threshold

BUG=aomedia:2392

Change-Id: Ibf03092f72ca9b0f2d4b749a52c5708db276f8c5

test/datarate_test.cc

diff --git a/test/datarate_test.cc b/test/datarate_test.cc
index b1f8fe8..8ea38f0 100644
--- a/test/datarate_test.cc
+++ b/test/datarate_test.cc
@@ -129,7 +129,7 @@
     cfg_.rc_target_bitrate = bitrate_array[GET_PARAM(4)];
     ResetModel();
     ASSERT_NO_FATAL_FAILURE(RunLoop(&video));
-    ASSERT_GE(effective_datarate_, cfg_.rc_target_bitrate * 0.74)
+    ASSERT_GE(effective_datarate_, cfg_.rc_target_bitrate * 0.72)
         << " The datarate for the file is lower than target by too much!";
     ASSERT_LE(effective_datarate_, cfg_.rc_target_bitrate * 1.25)
         << " The datarate for the file is greater than target by too much!";