Replace builds with buildCommand in vercel.json (#2329)

Co-authored-by: Nolan Lawson <nolan@nolanlawson.com>

bin/build-vercel-json.js

@@ -21,15 +21,8 @@ const JSON_TEMPLATE = {
   github: {
     silent: true
   },
-  builds: [
+  buildCommand: 'yarn build',
-    {
+  outputDirectory: '__sapper__/export',
-      src: 'package.json',
-      use: '@now/static-build',
-      config: {
-        distDir: '__sapper__/export'
-      }
-    }
-  ],
   routes: [
     {
       src: '^/service-worker\\.js$',

vercel.json

@@ -6,15 +6,8 @@
   "github": {
     "silent": true
   },
-  "builds": [
+  "buildCommand": "yarn build",
-    {
+  "outputDirectory": "__sapper__/export",
-      "src": "package.json",
-      "use": "@now/static-build",
-      "config": {
-        "distDir": "__sapper__/export"
-      }
-    }
-  ],
   "routes": [
     {
       "src": "^/service-worker\\.js$",