datarate test: Change threshold for rate targeting.

BUG=aomedia:2387

Change-Id: Id1840900b1d17694ad2d99c3d4eaf28649515afe
diff --git a/test/datarate_test.cc b/test/datarate_test.cc
index 856d4e8..9cc6f78 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 * 0.75)
+    ASSERT_GE(effective_datarate_, cfg_.rc_target_bitrate * 0.74)
         << " 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!";