Update CI script to use a different image

.gitlab-ci.yml

@@ -1,10 +1,10 @@
 image:
-  name: racket/racket:8.2-full
+  name: opensuse/tumbleweed
 
 default:
   before_script:
-    - apt-get update
-    - apt-get install -y make
+    - zypper refresh
+    - zypper install -y make racket
     - raco pkg install --deps search-auto goblins/
 
 stages:
@@ -18,8 +18,8 @@ compile:
 
 unit-tests:
   before_script:
-    - apt-get update
-    - apt-get install -y xvfb make
+    - zypper refresh
+    - zypper install -y xorg-x11-server-Xvfb make racket
     - Xvfb :4 -screen 0 1024x768x24 &
     - raco pkg install --deps search-auto goblins/
   stage: test