fix(report): include earl:result for documents that have no assertions

documents that pass automatic checks will have no assertions, but the earl:result object must be created for them anyway

fixes #120

src/report/axe2ace.js

@@ -67,7 +67,7 @@ const kbMap = {
 function  axe2ace(spineItem, axeResults) {
   winston.verbose(`Converting aXe results to ace for ${spineItem.relpath}`);
 
-    // the top-level assertion
+    // the content doc-level assertion
     const assertion = new builders.AssertionBuilder()
       .withSubAssertions()
       .withTestSubject(spineItem.relpath, spineItem.title);

src/report/report-builders.js

@@ -47,6 +47,8 @@ function withTestSubject(obj, url, title = '', identifier = '', metadata = null)
 class AssertionBuilder {
   constructor() {
     this._json = { '@type': 'earl:assertion' };
+    var result = new ResultBuilder('pass').build();
+    this.withResult(result); // default result until we know more
   }
   build() {
     return this._json;