.travis.yml: dump XML report from Robot Framework.

HTML report is really huge and the problem with truncated logs was appeared again. Adding a
sleep 5/sleep 10 didn't help, so I decided to get back to XML reports.

This commit reverts 2e5b67f and
49661ff commits and applies
a309046 again.

Author: php-coder

.travis.yml

@@ -40,7 +40,7 @@ after_failure:
   # Just encode it to a gzipped binary form and dump to console.
   - if fgrep -qs 'status="FAIL"' target/robotframework-reports/output.xml; then
       echo "===== REPORT START =====";
-      cat target/robotframework-reports/log.html | gzip -c | base64;
+      cat target/robotframework-reports/output.xml | gzip -c | base64;
       echo "===== REPORT END =====";
       sleep 5;
     fi