Ubuntu 16.04 is past its normal LTS lifespan, so let's switch to Ubuntu
20.04 instead, which is the latest regular LTS version.

Signed-off-by: brian m. carlson <redacted>
---
 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 526ecfe030..a1bc92893f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml

@@ -35,7 +35,7 @@ test:linux:
   parallel:
     matrix:
       - jobname: linux-old
-        image: ubuntu:16.04
+        image: ubuntu:20.04
         CC: gcc
       - jobname: linux-sha256
         image: ubuntu:latest