speedup CI

.travis.yml

@@ -1,7 +1,9 @@
 cache: cargo
 before_cache:
-    - find ./target/debug -maxdepth 1 -type f -delete
-    - rm -fr ./target/debug/{deps,.fingerprint}/{*ra_*,*test*,*gen_lsp*,*thread_worker*}
+    # ask Cargo to clean up artifacts for workspace crates
+    - cargo clean $(printf -- '--package %s ' $(cd crates; ls))
+    # Cargo doesn't clean up depinfo itself, do it manually
+    - find ./target/debug -maxdepth 2 -iname '*.d' -delete
     - rm -f  ./target/.rustc_info.json
 
 matrix:
@@ -14,6 +16,7 @@ matrix:
           script:
               - rustup component add rustfmt
               - rustup component add rust-src
+              - printf "\n\n[profile.dev]\ndebug = false\nopt-level = 1\n" >> Cargo.toml
               - cargo test --no-run  # let's measure compile time separately
               - cargo test
           env: