Remove build directory before building to avoid old artifacts bei… (#31)

package.json

@@ -19,6 +19,7 @@
  "test": "jest",
  "lint": "eslint .",
  "watch": "babel src -w --ignore **/*.test.js,integration -d build",
+ "prebuild": "rimraf build",
  "build": "babel src --ignore **/*.test.js,integration -d build",
  "prepublish": "yarn build",
  "format": "prettier --single-quote --trailing-comma all --write \"!(build)/**/*.js\""
@@ -48,7 +49,8 @@
  "eslint-plugin-prettier": "^3.0.1",
  "flow-bin": "^0.105.2",
  "jest": "^24.3.0",
- "prettier": "^1.13.7"
+ "prettier": "^1.13.7",
+ "rimraf": "^3.0.0"
  },
  "jest": {
  "watchPlugins": [

yarn.lock

@@ -4202,6 +4202,13 @@ rimraf@^2.5.4, rimraf@^2.6.1, rimraf@^2.6.3:
  dependencies:
  glob "^7.1.3"
 
+rimraf@^3.0.0:
+ version "3.0.0"
+ resolved "https://registry.npmjs.org/rimraf/-/rimraf-3.0.0.tgz#614176d4b3010b75e5c390eb0ee96f6dc0cebb9b"
+ integrity sha512-NDGVxTsjqfunkds7CqsOiEnxln4Bo7Nddl3XhS4pXg5OzwkLqJ971ZVAAnB+DDLnF76N+VnDEiBHaVV8I06SUg==
+ dependencies:
+ glob "^7.1.3"
+
 rsvp@^4.8.4:
  version "4.8.5"
  resolved "https://registry.yarnpkg.com/rsvp/-/rsvp-4.8.5.tgz#c8f155311d167f68f21e168df71ec5b083113734"