Fix watch command (#403)

package.json

@@ -39,6 +39,7 @@
     "rollup": "^0.41.0",
     "rollup-plugin-babel": "^2.6.1",
     "rollup-plugin-node-resolve": "^2.0.0",
+    "rollup-watch": "^3.2.2",
     "unicode-9.0.0": "~0.7.0"
   },
   "bin": {
@@ -56,7 +57,7 @@
     "test-only": "ava",
     "test-ci": "nyc npm run test-only",
     "changelog": "git log `git describe --tags --abbrev=0`..HEAD --pretty=format:' * %s (%an)' | grep -v 'Merge pull request'",
-    "watch": "npm run clean && cross-env BABEL_ENV=watch babel src --out-dir lib --watch"
+    "watch": "npm run clean && rollup -c --watch"
   },
   "nyc": {
     "include": [

yarn.lock

@@ -3265,6 +3265,10 @@ require-precompiled@^0.1.0:
   version "0.1.0"
   resolved "https://registry.yarnpkg.com/require-precompiled/-/require-precompiled-0.1.0.tgz#5a1b52eb70ebed43eb982e974c85ab59571e56fa"
 
+require-relative@0.8.7:
+  version "0.8.7"
+  resolved "https://registry.yarnpkg.com/require-relative/-/require-relative-0.8.7.tgz#7999539fc9e047a37928fa196f8e1563dabd36de"
+
 require-uncached@^1.0.2:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/require-uncached/-/require-uncached-1.0.3.tgz#4e0d56d6c9662fd31e43011c4b95aa49955421d3"
@@ -3343,6 +3347,12 @@ rollup-pluginutils@^1.5.0:
     estree-walker "^0.2.1"
     minimatch "^3.0.2"
 
+rollup-watch@^3.2.2:
+  version "3.2.2"
+  resolved "https://registry.yarnpkg.com/rollup-watch/-/rollup-watch-3.2.2.tgz#5e574232e9ef36da9177f46946d8080cb267354b"
+  dependencies:
+    require-relative "0.8.7"
+
 rollup@^0.41.0:
   version "0.41.4"
   resolved "https://registry.yarnpkg.com/rollup/-/rollup-0.41.4.tgz#a970580176329f9ead86854d7fd4c46de752aef8"