Only cache the `.cargo` directory on Travis

.travis.yml

@@ -5,18 +5,15 @@ rust:
   - beta
   - nightly
 
-cache: cargo
-# Reduce cache bloat 
+# Need to cache the whole `.cargo` directory to keep .crates.toml for
+# cargo-update to work
+cache:
+  directories:
+    - /home/travis/.cargo
+
+# But don't cache the cargo registry
 before_cache:
-  - rm -rfv "$TRAVIS_HOME/.cargo/registry/src"
-  - rm -rfv target/debug/incremental/{librespot,build_script_build}-*
-  - rm -rfv target/debug/.fingerprint/librespot-*
-  - rm -rfv target/debug/build/librespot-*
-  - rm -rfv target/debug/deps/liblibrespot-*
-  - rm -rfv target/debug/deps/librespot-*
-  - rm -rfv target/debug/{librespot,liblibrespot}.d
-  - rm -rfv target/debug/incremental/{build_script_build,librespot,librespot_core,librespot_connect,librespot_audio,librespot_metadata,librespot_playback,librespot_player,librespot_protocol}-*
-  - cargo clean -p librespot -p librespot-core -p librespot-connect -p librespot-audio -p librespot-metadata -p librespot-playback
+  - rm -rf /home/travis/.cargo/registry
   
 addons:
   apt: