Restrict the gpu_hang suite to R31.

The suite was constrained to R30 at creation time, but it missed
the R30->R31 branch split by a couple of builds, so it's in R31
instead.

BUG=None
TEST=None

Change-Id: I4a502307bfa76078a419e2c3049749021cc02469
Reviewed-on: https://gerrit.chromium.org/gerrit/65955
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
diff --git a/suite_scheduler.ini b/suite_scheduler.ini
index c44de90..85332d8 100644
--- a/suite_scheduler.ini
+++ b/suite_scheduler.ini
@@ -53,7 +53,7 @@
 [GpuHang]
 run_on: new_build
 suite: gpu_hang
-branch_specs: >=R30
+branch_specs: >=R31
 pool: suites
 
 [NightlyHwQual]