Remove preset-es2015 dependency (#1698)

* Switch rollup to babel env preset

Using the engine version from package.json

* Remove babel-preset-es2015 dependency

That darn thing was even in prod dependencies!

build/rollup.config.js

@@ -81,7 +81,12 @@ function genConfig (opts) {
           'external-helpers'
         ],
         presets: [
-          ['es2015', { modules: false }]
+          ['env', {
+            targets: {
+              node: '6.11.0'
+            },
+            modules: false
+          }]
         ],
         'env': {
           'test': {

package.json

@@ -69,7 +69,6 @@
     "autoprefixer": "^7.1.3",
     "babel-core": "^6.26.0",
     "babel-loader": "^7.1.2",
-    "babel-preset-es2015": "^6.24.1",
     "babel-preset-vue-app": "^1.3.0",
     "chalk": "^2.1.0",
     "chokidar": "^1.7.0",
@@ -129,7 +128,6 @@
     "babel-plugin-array-includes": "^2.0.3",
     "babel-plugin-external-helpers": "^6.22.0",
     "babel-plugin-istanbul": "^4.1.4",
-    "babel-preset-es2015": "^6.24.1",
     "codecov": "^2.3.0",
     "copy-webpack-plugin": "^4.0.1",
     "cross-env": "^5.0.5",