try to fix flow error in travis

Author: freedomlang

.travis.yml

@@ -1,12 +1,10 @@
 language: node_js
 node_js:
   - "8.10.0"
-before_install:
-  - npm install -g npm@latest
 script:
   - npm cache verify
   - ./node_modules/.bin/lerna exec -- npm cache verify
-  - ./node_modules/.bin/lerna bootstrap
+  - npm i packages/* && ./node_modules/.bin/lerna bootstrap --hoist
   - npm run build
   - npm run lint
   - npm run flow