Print exception stack when generating a test case fails.

test/generate-testcase.js

@@ -126,7 +126,7 @@ function runReadability(source, destPath, metadataDestPath) {
   try {
     var result = new Readability(uri, doc).parse();
   } catch (ex) {
-    console.error(ex);
+    console.error(ex.stack);
   }
   if (!result) {
     console.error("No content generated by readability, not going to write expected.html!");