feat: abandon yarn, move to npm (#417)

* feat: abandon yarn, move to npm

* fix: github workflows and package

* chore: update dependencies

Author: danigb

.github/workflows/tests.yml

@@ -17,6 +17,6 @@ jobs:
         uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node_version }}
-          cache: "yarn"
-      - run: yarn install
-      - run: yarn test:ci
+          cache: "npm"
+      - run: npm install
+      - run: npm run test:ci

docs/CONTRIBUTING.md

@@ -4,10 +4,9 @@ We're really glad you're reading this, because we need volunteers to help this p
 
 ## Prerequisites
 
-You will need node and yarn installed on your computer to run the code. And git to download it:
+You will need node installed on your computer to run the code. And git to download it:
 
 - [node](https://nodejs.org/en/download/)
-- [yarn](https://yarnpkg.com/)
 - [git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
 
 ## Download the code
@@ -16,8 +15,8 @@ To download the code, use git:
 
 ```bash
 git clone https://github.com/tonaljs/tonal
-yarn install
-yarn build
+npm install
+npm build
 ```
 
 ## Development
@@ -29,7 +28,7 @@ If you are adding new functionality or fixing a bug, please add a test for it.
 **Run test and build the library before submitting a pull request :pray:**
 
 ```bash
-yarn test:ci
+npm test:ci
 ```
 
 #### How to add a new module
@@ -40,7 +39,7 @@ To create a new module:
 - Add a new package.json inside the folder (see any of them as an example)
 - Add required dependencies to "dependencies" inside package.json. Ensure correct dependency versions. For example, if your module needs to use `tonal/core` look at core's package.json to see what version to use
 - Add your functionality and tests
-- Ensure everything works: run `yarn test:ci` at root folder
+- Ensure everything works: run `npm test:ci` at root folder
 - Create a pull request
 
 ## Release