remove unnessary install yarn command (actions#50)

kidonng · Danny McCormick · commit 57adacb752d5 · 2019-09-03T10:53:12.000-04:00
diff --git a/README.md b/README.md
@@ -71,7 +71,6 @@ steps:
   with:
     node-version: '10.x'
     registry-url: <registry url>
-- run: npm install -g yarn
 - run: yarn install
 - run: yarn publish
   env:
