fix: change debian version to newest

Author: casperr0

Makefile.tests

@@ -2,7 +2,7 @@ test: run_builds run_functional_tests
 
 run_builds:
 	docker run --rm -v "$(WORKDIR)":/var/tmp centos:7 /bin/bash -ex "/var/tmp/tests/build_rpm.sh"
-	docker run --rm -v "$(WORKDIR)":/var/tmp debian:7 /bin/bash -ex "/var/tmp/tests/build_deb.sh"
+	docker run --rm -v "$(WORKDIR)":/var/tmp debian:9 /bin/bash -ex "/var/tmp/tests/build_deb.sh"
 
 run_functional_tests:
 	docker run --rm -v "$(WORKDIR)":/var/tmp centos:6 /bin/bash -ex "/var/tmp/tests/check.sh"