chore: drop node 4 support (#97)

BREAKING CHANGE:

Author: DominicKramer

handwritten/nodejs-logging-winston/.circleci/config.yml

@@ -3,12 +3,10 @@ workflows:
   version: 2
   tests:
     jobs: &workflow_jobs
-      - node4:
+      - node6:
           filters: &all_commits
             tags:
               only: /.*/
-      - node6:
-          filters: *all_commits
       - node8:
           filters: *all_commits
       - node9:
@@ -17,15 +15,13 @@ workflows:
           filters: *all_commits
       - lint:
           requires:
-            - node4
             - node6
             - node8
             - node9
             - node10
           filters: *all_commits
       - docs:
           requires:
-            - node4
             - node6
             - node8
             - node9
@@ -62,9 +58,9 @@ workflows:
               only: master
     jobs: *workflow_jobs
 jobs:
-  node4:
+  node6:
     docker:
-      - image: 'node:4'
+      - image: 'node:6'
         user: node
     steps: &unit_tests_steps
       - checkout
@@ -95,11 +91,6 @@ jobs:
           name: Submit coverage data to codecov.
           command: node_modules/.bin/codecov
           when: always
-  node6:
-    docker:
-      - image: 'node:6'
-        user: node
-    steps: *unit_tests_steps
   node8:
     docker:
       - image: 'node:8'

handwritten/nodejs-logging-winston/package.json

@@ -5,7 +5,7 @@
   "license": "Apache-2.0",
   "author": "Google Inc.",
   "engines": {
-    "node": ">=4.0.0"
+    "node": ">=6.0.0"
   },
   "repository": "googleapis/nodejs-logging-winston",
   "main": "./build/src/index.js",