Merge pull request #32 from chrisfilo/enh/travis_cache

enable travis cache

.travis.yml

@@ -1,7 +1,10 @@
 language: node_js
 node_js:
   - "10"
+cache:
+  directories:
+  - node_modules # NPM packages
 before_script:
-  - npm install -g remark-cli@5.0.0 remark-lint@6.0.2 remark-preset-lint-recommended@3.0.2 remark-preset-lint-markdown-style-guide@2.1.2
+  - npm install remark-cli@5.0.0 remark-lint@6.0.2 remark-preset-lint-recommended@3.0.2 remark-preset-lint-markdown-style-guide@2.1.2
 script:
   - remark src/*.md src/*/*.md --frail