chore: replace yarn with npm

Author: nickserv

Diff for: .npmrc

@@ -0,0 +1 @@
+package-lock=false

Diff for: .travis.yml

@@ -1,28 +1,18 @@
 sudo: false
 language: node_js
-cache:
-  yarn: true
-  directories:
-    - "~/.npm"
 notifications:
   email: false
 node_js:
   - '10'
   - '12'
-env:
-  global:
-    - PATH=$HOME/.yarn/bin:$PATH
-before_install:
-  - curl -o- -L https://yarnpkg.com/install.sh | bash
-install: yarn
-script: yarn validate
+script: npm run validate
 jobs:
   include:
     - stage: release
       node_js: '12'
       deploy:
         provider: script
-        script: yarn test:update && npx codecov && npx semantic-release
+        script: npm run test:update && npx codecov && npx semantic-release
         skip_cleanup: true
 branches:
   only: master

Diff for: package.json

@@ -90,17 +90,17 @@
   },
   "lint-staged": {
     "README.md": [
-      "yarn toc",
+      "npm run toc",
       "prettier --parser markdown --write",
       "git add"
     ],
     ".all-contributorsrc": [
-      "yarn contributors:generate",
+      "npm run contributors:generate",
       "git add"
     ],
     "**/*.js": [
-      "yarn lint",
-      "yarn test",
+      "npm run lint",
+      "npm test",
       "git add"
     ]
   },