source-map: Cover ast2SourceNode completely

Author: Mingun

test/api/plugin-api.spec.js

@@ -76,6 +76,10 @@ describe("plugin API", () => {
             "start = .* {",
             "  return {",
             "    type: 'grammar',",
+            "    initializer: {",
+            "      type: 'initializer',",
+            "      code: ['/* included for cover ast2SourceNode in the generate-js pass */'],",
+            "    },",
             "    rules: [",
             "      {",
             "        type: 'rule',",