switch from babel to buble

package.json

@@ -53,6 +53,7 @@
     "remap-istanbul": "^0.5.1",
     "rollup": "^0.20.2",
     "rollup-plugin-babel": "^1.0.0",
+    "rollup-plugin-buble": "^0.5.0",
     "rollup-plugin-node-resolve": "^1.5.0",
     "rollup-plugin-replace": "^1.0.1",
     "sander": "^0.4.0",

rollup.config.js

@@ -1,5 +1,5 @@
 import { readFileSync } from 'fs';
-import babel from 'rollup-plugin-babel';
+import buble from 'rollup-plugin-buble';
 import npm from 'rollup-plugin-node-resolve';
 import replace from 'rollup-plugin-replace';
 
@@ -22,7 +22,7 @@ export default {
 	entry: 'src/rollup.js',
 	format: 'cjs',
 	plugins: [
-		babel({
+		buble({
 			include: [ 'src/**', 'node_modules/acorn/**' ]
 		}),