add build:clean script

package.json

@@ -10,7 +10,8 @@
     "url": "https://github.com/garetmckinley"
   },
   "scripts": {
-    "build": "npm run build:lib && npm run build:dist",
+    "build": "npm run build:clean && npm run build:lib && npm run build:dist",
+    "build:clean": "rimraf dist/ lib/",
     "build:lib": "babel src --out-dir lib",
     "build:dist": "rollup -c && rollup -c --environment PRODUCTION",
     "clean": "rm -rf dist && rm -rf lib",
@@ -60,6 +61,7 @@
     "eslint-plugin-react": "^7.11.1",
     "react": "^16.4.2",
     "react-dom": "^16.4.2",
+    "rimraf": "^3.0.0",
     "rollup": "^0.66.2",
     "rollup-plugin-babel": "^3.0.7",
     "rollup-plugin-commonjs": "^9.1.6",

yarn.lock

@@ -8618,6 +8618,13 @@ rimraf@2, rimraf@^2.2.8, rimraf@^2.5.4, rimraf@^2.6.1, rimraf@^2.6.2:
   dependencies:
     glob "^7.1.3"
 
+rimraf@^3.0.0:
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/rimraf/-/rimraf-3.0.0.tgz#614176d4b3010b75e5c390eb0ee96f6dc0cebb9b"
+  integrity sha512-NDGVxTsjqfunkds7CqsOiEnxln4Bo7Nddl3XhS4pXg5OzwkLqJ971ZVAAnB+DDLnF76N+VnDEiBHaVV8I06SUg==
+  dependencies:
+    glob "^7.1.3"
+
 rimraf@~2.5.1, rimraf@~2.5.4:
   version "2.5.4"
   resolved "https://registry.yarnpkg.com/rimraf/-/rimraf-2.5.4.tgz#96800093cbf1a0c86bd95b4625467535c29dfa04"