refactor: import rollup

rollup.config.js

@@ -0,0 +1,71 @@
+import shim from 'rollup-plugin-shim'
+import babel from 'rollup-plugin-babel'
+import {uglify} from 'rollup-plugin-uglify'
+import pkg from './package.json'
+import nodeResolve from 'rollup-plugin-node-resolve'
+
+const fake = {fs: `export default {}`, path: `export default {}`}
+const version = process.env.VERSION || pkg.version
+const sourcemap = true
+const banner = `/*
+ * liquidjs@${version}, https://github.com/liquidjs
+ * (c) 2016-${new Date().getFullYear()} harttle
+ * Released under the MIT License.
+ */`
+const treeshake = {
+  propertyReadSideEffects: false
+}
+const input = 'src/index.js'
+
+const babelConf = {
+  babelrc: false,
+  'presets': [['env', {'modules': false}]],
+  'plugins': ['external-helpers']
+}
+
+export default [{
+  output: [{
+    file: 'dist/liquid.common.js',
+    name: 'Liquid',
+    format: 'cjs',
+    sourcemap,
+    banner
+  }],
+  external: ['path', 'fs'],
+  plugins: [
+    nodeResolve(),
+    babel(babelConf)
+  ],
+  treeshake,
+  input
+}, {
+  output: [{
+    file: 'dist/liquid.js',
+    name: 'Liquid',
+    format: 'umd',
+    sourcemap,
+    banner
+  }],
+  plugins: [
+    shim(fake),
+    nodeResolve(),
+    babel(babelConf)
+  ],
+  treeshake,
+  input
+}, {
+  output: [{
+    file: 'dist/liquid.min.js',
+    name: 'Liquid',
+    format: 'umd',
+    sourcemap
+  }],
+  plugins: [
+    shim(fake),
+    nodeResolve(),
+    babel(babelConf),
+    uglify()
+  ],
+  treeshake,
+  input
+}]