Try to use pip cache in tox

.gitlab-ci.yml

@@ -10,11 +10,11 @@ variables:
   #  - pip: tox, coverage
   #  - apt: ghostscript
   PY35_IMAGE: twiggers/python-thalia:3.5
+  PIP_CACHE_DIR: "${CI_PROJECT_DIR}/pip-cache"
 
 pep8:
   image: $PY35_IMAGE
   before_script:
-    - export PIP_CACHE_DIR="pip-cache"
   script:
     - tox -e flake8
 
@@ -22,8 +22,6 @@ pep8:
   services:
     - postgres:latest
   before_script:
-    - export PIP_CACHE_DIR="pip-cache"
-    - mkdir -p pip-cache
     - git log -1
   script:
     - tox -e ${PYTHON_VERSION}-${DJANGO_VERSION}
@@ -52,6 +50,6 @@ docs:
 cache:
   key: "$CI_JOB_NAME"
   paths:
-    - pip-cache
+    - "${PIP_CACHE_DIR}"
 
 # vim: set sw=2 ts=2 et :

tox.ini

@@ -22,7 +22,9 @@ deps =
     django11: django>=1.11b1,<1.12
     {env:CI_DEPS:}
 
-passenv = GITLAB_CI
+passenv =
+    GITLAB_CI
+    PIP_CACHE_DIR
 whitelist_externals=
     sed
     cp
@@ -35,3 +37,5 @@ deps= flake8
 skip_install=True
 commands=
     flake8 .
+passenv =
+    PIP_CACHE_DIR