bug in report.html template

originally reported as https://github.com/inorton/junit2html/issues/48

In the main template file report.html two different syntax are used to asses if a test case has failures

works:

{% if test.failed() %}

always true:

{% if test.failed %}

It seems second variant will return true even if no failures, or the branch statement be disregarded, because for me this caused elements associated with failures to be printed into the output file, despite no failures in the test. Adding the brackets fixed it.