cache joinmarket deps on travis

.travis.yml

@@ -11,7 +11,9 @@ addons:
 matrix:
   include:
     - os: osx
+      env: PIP_DOWNLOAD_CACHE=$HOME/Library/Caches/pip
     - os: linux
+      env: PIP_DOWNLOAD_CACHE=$HOME/.cache/pip
     - os: linux
       services: docker
       env: DOCKER_IMG_JM=xenial
@@ -33,9 +35,15 @@ before_install:
   - on_docker(){ if [ -n "$DOCKER_IMG_JM" ]; then $@ ; fi; }
 cache:
   directories:
-    $HOME/downloads
+   - $HOME/downloads
+   - $HOME/.cache/pip
+   - $HOME/Library/Caches/pip
 install:
+  - mkdir -p "$HOME/downloads"
+  - mkdir -p "$TRAVIS_BUILD_DIR/deps/cache/"
+  - find "$HOME/downloads" -type f -exec cp -v {} "$TRAVIS_BUILD_DIR/deps/cache/" \;
   - on_host ./install.sh --develop --no-gpg-validation
+  - on_host find "$TRAVIS_BUILD_DIR/deps/cache/" -type f -exec cp -v {} "$HOME/downloads/" \;
 before_script:
   - on_host source jmvenv/bin/activate
 script: