ci: clean up image

rust-bindings/rust/.gitlab-ci.yml

@@ -1,4 +1,4 @@
-image: rust:latest
+image: rust:1-buster
 
 variables:
   SCCACHE_URL: https://github.com/mozilla/sccache/releases/download/0.2.8/sccache-0.2.8-x86_64-unknown-linux-musl.tar.gz
@@ -8,9 +8,9 @@ variables:
   RUSTC_WRAPPER: sccache
 
 before_script:
-- echo deb http://ftp.debian.org/debian stretch-backports main > /etc/apt/sources.list.d/backports.list
+# TODO: use libostree from unstable
 - apt-get update
-- apt-get install -y -t stretch-backports cmake libostree-dev
+- apt-get install -y libostree-dev
 - wget -O - ${SCCACHE_URL} | tar -C /usr/bin/ -xz --wildcards --strip-components=1 '*/sccache'
 
 cache: