fix: Update node version requirement (#646)

* fix: specify lowest node version in package.json The lowest version of node required by explicit dependencies is ^8.12.0 specified by Execa * test: run tests on node 8, 10 and 12

Author: Iiro Jäppinen

.appveyor.yml

@@ -4,8 +4,8 @@
 
 environment:
  matrix:
+ - nodejs_version: '12'
  - nodejs_version: '10'
- - nodejs_version: '9'
  - nodejs_version: '8'
 
 matrix:

.travis.yml

@@ -4,8 +4,8 @@
 
 language: node_js
 node_js:
+ - '12'
  - '10'
- - '9'
  - '8'
 
 before_install: yarn global add greenkeeper-lockfile@1

index.js

@@ -6,7 +6,7 @@ const pkg = require('./package.json')
 require('please-upgrade-node')(
  Object.assign({}, pkg, {
  engines: {
- node: '>=8.6.0'
+ node: '>=8.12.0'
  }
  })
 )