use archlinux image for tests

* switching from alpine-cmake that lacked valgrind

Signed-off-by: surtur <a_mirre@utb.cz>

.drone.yml

@@ -6,10 +6,11 @@ platform:
   arch: amd64
 
 steps:
-- name: test build
+- name: test build + valgrind
   pull: if-not-exists
-  image: spritsail/alpine-cmake:edge
+  image: archlinux
   commands:
+  - pacman -Sy --noconfirm cmake make gcc valgrind
   - cmake CMakeLists.txt
   - make
   - valgrind --log-file=valgrind_output ./pjc-0x02 < ./test_input > output