Change to use buildCommand option of shipjs. (#102)

It seems that the build runs by default when the buildCommand option is removed.
https://community.algolia.com/shipjs/reference/all-config.html#buildcommand

Author: ota-meshi

package.json

@@ -100,7 +100,6 @@
     "lint": "eslint --ext js,ts lib scripts tests docs/.vuepress --ignore-pattern \"!.*\"",
     "lint:docs": "eslint --ext js,vue,md docs --ignore-pattern \"!.*\"",
     "release:prepare": "shipjs prepare",
-    "prerelease:trigger": "yarn build",
     "release:trigger": "shipjs trigger",
     "test": "mocha --require ts-node/register \"./tests/**/*.ts\"",
     "test:debug": "mocha --require ts-node/register --inspect \"./tests/**/*.ts\"",

ship.config.js

@@ -5,7 +5,7 @@ const path = require('path')
 const read = promisify(fs.readFile)
 const write = fs.writeFileSync
 
-function extractSpecificChangelog (changelog, version) {
+function extractSpecificChangelog(changelog, version) {
   if (!changelog) {
     return null
   }
@@ -18,8 +18,12 @@ function extractSpecificChangelog (changelog, version) {
   return matches ? matches[1] : null
 }
 
-async function commitChangelog (current, next) {
-  const { stdout } = await execa('npx', ['lerna-changelog', '--next-version', `v${next}`])
+async function commitChangelog(current, next) {
+  const { stdout } = await execa('npx', [
+    'lerna-changelog',
+    '--next-version',
+    `v${next}`
+  ])
   const escapedVersion = next.replace(/\./g, '\\.')
   const regex = new RegExp(
     `(#+?\\s\\[?v?${escapedVersion}\\]?[\\s\\S]*?)(#+?\\s\\[?v?\\d\\.\\d\\.\\d\\]?)`,
@@ -35,23 +39,16 @@ module.exports = {
   mergeStrategy: { toSameBranch: ['master'] },
   monorepo: undefined,
   updateChangelog: false,
-  buildCommand: ({ isYarn }) => undefined,
   beforeCommitChanges: ({ nextVersion, exec, dir }) => {
     return new Promise(resolve => {
       const pkg = require('./package.json')
       commitChangelog(pkg.version, nextVersion).then(resolve)
     })
   },
-  formatCommitMessage: ({
-    version,
-    releaseType,
-    mergeStrategy,
-    baseBranch
-  }) => `${releaseType} release v${version}`,
-  formatPullRequestTitle: ({
-    version,
-    releaseType
-  }) => `${releaseType} release v${version}`,
+  formatCommitMessage: ({ version, releaseType, mergeStrategy, baseBranch }) =>
+    `${releaseType} release v${version}`,
+  formatPullRequestTitle: ({ version, releaseType }) =>
+    `${releaseType} release v${version}`,
   shouldRelease: () => true,
   releases: {
     extractChangelog: ({ version, dir }) => {