[IMP] component: allow dynamic root nodes

closes #283

tests/router/__snapshots__/Link.test.ts.snap

@@ -5,11 +5,13 @@ exports[`Link component can render simple cases 1`] = `
 ) {
     let utils = this.constructor.utils;
     let owner = context;
+    let result;
     var h = this.h;
     let _1 = utils.toObj({'router-link-active':context['isActive']});
     var _2 = context['href'];
     let c3 = [], p3 = {key:3,attrs:{href: _2},class:_1,on:{}};
     var vn3 = h('a', p3, c3);
+    result = vn3;
     if (!context['navigate']) {
         throw new Error('Missing handler \\\\'' + 'navigate' + \`\\\\' when evaluating template '__owl__-router-link'\`)
     }
@@ -19,6 +21,6 @@ exports[`Link component can render simple cases 1`] = `
     if (slot4) {
         slot4.call(this, context.__owl__.parent, Object.assign({}, extra, {parentNode: c3, vars: extra.vars, parent: owner}));
     }
-    return vn3;
+    return result;
 }"
 `;