travis: pip6 download cache

.travis.yml

@@ -3,15 +3,13 @@ compiler:
     - gcc
 env:
     global:
-        - PIP_DOWNLOAD_CACHE="${HOME}/.pip-cache"
         - PATH="${PATH}:${HOME}/.local/bin"
         - PKG_CONFIG_PATH="${HOME}/fakeroot/lib/pkgconfig"
         - LD_LIBRARY_PATH="${HOME}/fakeroot/lib"
         - CFLAGS="${CFLAGS} -O0 -g -DNDEBUG"
 before_script:
     - ./scripts/bootstrap-depends.sh ${HOME}/fakeroot
-    - pip install --user travis -r tests/pydnstest/requirements.txt
-    - pip install --user travis cpp-coveralls
+    - pip install --user travis -r tests/pydnstest/requirements.txt cpp-coveralls
 script:
     - make check COVERAGE=1 LDFLAGS="-L${HOME}/fakeroot/lib"
     - coveralls -i lib -x ".c" --gcov-options '\-lp'
@@ -19,4 +17,4 @@ sudo: false
 cache:
     directories:
     - ${HOME}/fakeroot
-    - ${HOME}/.pip-cache
+    - ${HOME}/.cache/pip