build dir for pip

bin/steps/pip-install

@@ -8,7 +8,7 @@ puts-cmd "pip install -r requirements.txt"
 cd /app
 
 set +e
-/app/.heroku/python/bin/pip install -r requirements.txt --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee $WARNINGS_LOG | cleanup | indent
+/app/.heroku/python/bin/pip install -r $BUILD_DIR/requirements.txt --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee $WARNINGS_LOG | cleanup | indent
 PIP_STATUS="${PIPESTATUS[0]}"
 set -e