chore: update testing matrix

BREAKING CHANGE: removed Node 4/5 from testing matrix

Author: Benjamin

Diff for: .travis.yml

@@ -1,7 +1,7 @@
 language: node_js
 node_js:
-  - "4"
-  - "5"
+  - "6"
+  - "10"
   - "stable"
 before_script:
   - git config --global user.name 'Travis-CI'

Diff for: appveyor.yml

@@ -1,6 +1,6 @@
 environment:
   matrix:
-    - nodejs_version: '6'
+    - nodejs_version: '10'
 install:
   - ps: Install-Product node $env:nodejs_version
   - git config --global user.name 'Appveyor'