BUGFIX: Revert the switch to the internal flow gen-flow-files command…

… to reduce the number of dependencies

This reverts commit fb11dff.

package.json

@@ -31,7 +31,7 @@
     "jest:coverage": "npm run jest -- --coverage",
     "build:clean": "rimraf dist",
     "build:babel": "babel src --out-dir dist --ignore spec.js",
-    "build:flow": "flow gen-flow-files src --out-dir dist",
+    "build:flow": "flow-copy-source -v src dist --ignore='*.spec.js'",
     "build": "npm run build:babel && npm run build:flow",
     "dev": "nodemon --quiet --watch src --exec 'npm run build'",
     "flow": "flow",
@@ -60,6 +60,7 @@
     "babel-cli": "^6.26.0",
     "eslint": "^4.9.0",
     "flow-bin": "^0.58.0",
+    "flow-copy-source": "^1.2.1",
     "flow-typed": "^2.2.1",
     "husky": "^0.14.3",
     "jest": "^21.0.2",