drop support to npm, yarn is better

[rodrigondec]

Yarn is better at solving dependency conflicts.

By using yarn ONLY, the conflict is automagically resolved.

Related Issue

• fixes Possible dependency conflict #412

Proposed Changes

• use yarn instead of npm
• drop support to npm on Makefile

[rodrigondec]

At this point, the conflict is a warning on yarn. But yarn solves the problem by itself.

Should I tackle the versions to avoid the warning too?

yarn install v1.22.19
warning ../package.json: No license field
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
warning " > eslint-watch@5.1.2" has incorrect peer dependency "eslint@>=4 <6.0.0".
warning " > estraverse-fb@1.3.2" has unmet peer dependency "estraverse@*".
warning " > react-markdown@4.3.1" has incorrect peer dependency "react@^15.0.0 || ^16.0.0".
warning " > react-tap-event-plugin@3.0.3" has incorrect peer dependency "react@^16.0.0-0 < 16.4.0".
warning " > react-tap-event-plugin@3.0.3" has incorrect peer dependency "react-dom@^16.0.0-0 < 16.4.0".
warning " > react-test-renderer@16.14.0" has incorrect peer dependency "react@^16.14.0".
[4/4] Building fresh packages...
$ yarn run build
yarn run v1.22.19
warning ../package.json: No license field
$ yarn run build:lib && gulp sass && gulp sass-copy
warning ../package.json: No license field
$ babel src/ -d lib/

[lucianapepelucio]

LGTM