feat($cli): allow unknown options in dev and build command

Author: ulivz

packages/@vuepress/cli/index.js

@@ -41,6 +41,7 @@ exports.bootstrap = function ({
 
   cli
     .command('dev [targetDir]', 'start development server')
+    .allowUnknownOptions()
     .option('-p, --port <port>', 'use specified port (default: 8080)')
     .option('-t, --temp <temp>', 'set the directory of the temporary file')
     .option('-c, --cache [cache]', 'set the directory of cache')
@@ -73,6 +74,7 @@ exports.bootstrap = function ({
 
   cli
     .command('build [targetDir]', 'build dir as static site')
+    .allowUnknownOptions()
     .option('-d, --dest <dest>', 'specify build output dir (default: .vuepress/dist)')
     .option('-t, --temp <temp>', 'set the directory of the temporary file')
     .option('-c, --cache [cache]', 'set the directory of cache')