build(babel-preset-env): configured babel to use the env preset

chose a target of node-8 since much lower would require transpilation of async/await

BREAKING CHANGE: the bundles now transpile with a target of node8, so lower versions of node are no longer supported

.babelrc

@@ -1,3 +1,4 @@
 {
-  "presets": ["es2015-node", "stage-3"]
+  "presets": [["env", {"targets": {"node": "current"}}]],
+  "plugins": [["transform-object-rest-spread", {"useBuiltIns": true}]]
 }

package.json

@@ -51,9 +51,8 @@
     "@travi/any": "1.7.1",
     "@travi/eslint-config-travi": "1.6.6",
     "babel-core": "6.26.0",
-    "babel-preset-es2015-node": "6.1.1",
-    "babel-preset-es2015-rollup": "3.0.0",
-    "babel-preset-stage-3": "6.24.1",
+    "babel-plugin-transform-object-rest-spread": "6.26.0",
+    "babel-preset-env": "1.6.1",
     "chai": "4.1.2",
     "chai-as-promised": "7.1.1",
     "codecov": "3.0.0",

rollup.config.js

@@ -21,7 +21,8 @@ export default {
     babel({
       babelrc: false,
       exclude: ['./node_modules/**'],
-      presets: ['es2015-rollup', 'stage-3']
+      presets: [['env', {modules: false, targets: {node: 8}}]],
+      plugins: [['transform-object-rest-spread', {useBuiltIns: true}]]
     })
   ],
   output: [