add cache to Travis CI

.travis.yml

@@ -8,6 +8,9 @@ branches:
   only:
   - master
   - develop
+cache:
+  directories:
+  - /tmp/elpa
 env:
   global:
   - secure: "M8NF1Uw7VGkLdNmWiUF4T+VOJXwN8KCKVQb45/BWVpGm88Rcfom/9bxRTUme8VYuzIavph32QF+P9KyhX8aj2p2FMItNnxiEySzap5UrLrNiwB6ZxbQglMJj0yMQKASynNBai9KKI7mYlsM5jRpFJ9OSgj7Ko00RIFpO3EpJ+kE="

.travisci/pub_prep.sh

@@ -36,7 +36,9 @@ echo $base_revision > /tmp/base_revision
 echo "Base revision $base_revision"
 
 fold_start "FORMATTING_DOCUMENTATION"
-docker run --rm \
+docker run \
+       --rm \
+       -v "/tmp/elpa/:/root/.emacs.d/elpa/" \
        -v "${TRAVIS_BUILD_DIR}/.ci/spacedoc-cfg.edn":/opt/spacetools/spacedoc-cfg.edn \
        -v "${TRAVIS_BUILD_DIR}":/tmp/docs/ \
        jare/spacetools docfmt /tmp/docs/
@@ -67,7 +69,9 @@ cp ./.travisci/.spacemacs ~/
 ln -sf ~/.emacs.d "${TRAVIS_BUILD_DIR}"
 
 fold_start "INSTALLING_DEPENDENCIES"
-docker run --rm \
+docker run \
+       --rm \
+       -v "/tmp/elpa/:/root/.emacs.d/elpa/" \
        -v "${TRAVIS_BUILD_DIR}:/root/.emacs.d" \
        -v "${TRAVIS_BUILD_DIR}/.travisci/.spacemacs:/root/.spacemacs" \
        --entrypoint emacs \
@@ -79,7 +83,9 @@ fi
 fold_end "INSTALLING_DEPENDENCIES"
 
 fold_start "EXPORTING_DOCUMENTATION"
-docker run --rm \
+docker run \
+       --rm \
+       -v "/tmp/elpa/:/root/.emacs.d/elpa/" \
        -v "${TRAVIS_BUILD_DIR}:/root/.emacs.d" \
        -v "${TRAVIS_BUILD_DIR}/.travisci/.spacemacs:/root/.spacemacs" \
        --entrypoint emacs \