add options.ssr

This allows setting custom vue renderer options. including:
- shouldPreload(file, type)
- runInNewContext
- directives

https://ssr.vuejs.org/en/api.html#renderer-options

lib/build.js

@@ -486,10 +486,10 @@ function createRenderer (bundle, manifest) {
       maxAge: 1000 * 60 * 15
     }))
   }
-  this.renderer = createBundleRenderer(bundle, {
+  this.renderer = createBundleRenderer(bundle, Object.assign({
     cache: cacheConfig,
     clientManifest: manifest
-  })
+  }, this.options.ssr))
   this.renderToString = pify(this.renderer.renderToString)
   this.renderToStream = this.renderer.renderToStream
 }