Fix npm warnings

npm WARN eslint-config-react-app@3.0.0-next.66cc7a90 requires a peer of eslint@^4.1.1 but none is installed. You must install peer dependencies yourself. npm WARN eslint-config-react-app@3.0.0-next.66cc7a90 requires a peer of eslint-plugin-flowtype@^2.34.1 but none is installed. You must install peer dependencies yourself.