chore(travis): cache dependencies

KyleRoss · KyleRoss · commit c622dd375a61 · 2019-03-19T20:54:52.000-04:00
diff --git a/.travis.yml b/.travis.yml
@@ -6,6 +6,7 @@ node_js:
   - "10"
   - "8"
   - "6"
+cache: npm
 after_success: 'npm run coveralls'
 
 os:
