Build flit in Gitlab CI

.gitlab-ci.yml

+image: "r.lcr.gr/microhacks/bevy-builder"
+
+build-linux:
+  stage: build
+  before_script:
+    - export CARGO_HOME="${CI_PROJECT_DIR}/.cargo"
+    - export PATH="${CI_PROJECT_DIR}/.cargo/bin:$PATH"
+  cache:
+    key: build-flit-linux
+    paths:
+      - .cargo/registry/cache
+      - .cargo/registry/index
+      - .cargo/git/db
+      - .cargo/bin/
+      - target/
+  script:
+    - cargo build --release
+    - strip target/release/flit
+  artifacts:
+    name: flit.linux.x86
+    paths:
+      - target/release/flit
+    expire_in: 1 day
+  only:
+    - trunk