fix: fix absolute path for outputDir option

Author: yyx990803

packages/@vue/cli-service/__tests__/Service.spec.js

@@ -91,7 +91,7 @@ test('handle option baseUrl and outputDir correctly', () => {
   })
   const service = createMockService()
   expect(service.projectOptions.baseUrl).toBe('https://foo.com/bar/')
-  expect(service.projectOptions.outputDir).toBe('public')
+  expect(service.projectOptions.outputDir).toBe('/public')
 })
 
 test('load project options from vue.config.js', () => {

packages/@vue/cli-service/lib/Service.js

@@ -336,6 +336,6 @@ function ensureSlash (config, key) {
 
 function removeSlash (config, key) {
   if (typeof config[key] === 'string') {
-    config[key] = config[key].replace(/^\/|\/$/g, '')
+    config[key] = config[key].replace(/\/$/g, '')
   }
 }