Bug Fix for bug 4063.

This is a bug fix for 4063. "Notice: Array to string conversion" when downloading CSV or TSV files from Visitor Log in 1.12. 

Some custom variables are in the $csv array as arrays themselves. Line 283 was trying to handle this array as a string and was throwing the error. This fix parses the array into a string prior to the string formatting step. The csv will successfully download with this fix. Tested on PHP 5.4.13. 

Pull request for master. 

The bug is reproducible with a clean install and generated data using the plugin. The route is address to get the bug is:

index.php?module=API&method=Live.getLastVisitsDetails&format=CSV&idSite=1&period=day&date=yesterday&expanded=1&translateColumnNames=1&language=en&filter_limit=100