export flow types in build (without test folders) (#412)

* export flow types in build (without test folders)

Another implementation of @nmn PR

Flow types very needed to avoid this trash: https://github.com/nodkz/graphql-compose/blob/master/src/definition.js (and graphql-js as git submodule) 
Also solved @nmn issue #400

FYI `npm run cp-flow` correctly works if sub-folders exist in `dist/` otherwise it prints `No such file or directory`.

* Copy source files with `.flow` extension in build proccess

* Move from `master` flag `--optional runtime` for build script

Author: nodkz

package.json

@@ -27,7 +27,8 @@
     "lint": "eslint src || (printf '\\033[33mTry: \\033[7m npm run lint -- --fix \\033[0m\\n' && exit 1)",
     "check": "flow check",
     "check-cover": "for file in {src/*.js,src/**/*.js}; do echo $file; flow coverage $file; done",
-    "build": "babel src --ignore __tests__ --out-dir dist/ && cp package.json dist/",
+    "build": "babel src --optional runtime --ignore __tests__ --out-dir dist/ && cp package.json dist/ && npm run build-dot-flow",
+    "build-dot-flow": "find ./src -name '*.js' -not -path '*/__*' | while read filepath; do cp $filepath `echo $filepath | sed 's/\\\/src\\\//\\\/dist\\\//g'`.flow; done",
     "watch": "babel-node ./resources/watch.js",
     "cover": "babel-node ./node_modules/.bin/isparta cover --root src --report html _mocha -- $npm_package_options_mocha",
     "cover:lcov": "babel-node ./node_modules/.bin/isparta cover --root src --report lcovonly _mocha -- $npm_package_options_mocha",