Set Node 8 as minimum node version officially supported

Author: tleunen

.babelrc

@@ -4,7 +4,7 @@
       "@babel/preset-env",
       {
         "targets": {
-          "node": 6
+          "node": 8
         },
         "loose": true
       }

.circleci/config.yml

@@ -1,16 +1,5 @@
 version: 2
 jobs:
-  test_with_node_6:
-    docker:
-      - image: circleci/node:6
-    steps:
-      - checkout
-      - run:
-          name: Install dependencies
-          command: npm install
-      - run:
-          name: Test
-          command: npm test
   test_with_node_8:
     docker:
       - image: circleci/node:8
@@ -65,7 +54,6 @@ workflows:
   version: 2
   test_all:
     jobs:
-      - test_with_node_6
       - test_with_node_8
       - test_with_node_9
       - test_with_node_10

appveyor.yml

@@ -1,6 +1,5 @@
 environment:
   matrix:
-    - nodejs_version: '6'
     - nodejs_version: '8'
     - nodejs_version: '9'
     - nodejs_version: '10'