chore(travis): drop builds in Node <4

.travis.yml

@@ -2,17 +2,13 @@ sudo: false
 language: node_js
 cache:
   directories:
-  - node_modules
+  - $HOME/.npm
 notifications:
   email: false
 node_js:
-- 5
-- 4
-- iojs
-- '0.12'
-- '0.10'
-before_install:
-- npm i -g npm@^2.0.0
+- 8 # stable
+- 6 # LTS
+- 4 # maintenance
 before_script:
 - npm prune
 after_success:
@@ -20,3 +16,6 @@ after_success:
 - npm run semantic-release
 services:
 - couchdb
+branches:
+  except:
+  - /^v\d+\.\d+\.\d+$/