feat: bump default less-loader version (#4468)

Resolves #4454

(cherry picked from commit 55e1c3c)

Author: haoqunjiang

packages/@vue/cli-service/generator/index.js

@@ -50,7 +50,7 @@ module.exports = (api, options) => {
       },
       less: {
         'less': '^3.0.4',
-        'less-loader': '^4.1.0'
+        'less-loader': '^5.0.0'
       },
       stylus: {
         'stylus': '^0.54.5',