Hello,
I guess it was detected by WebShield (which can bee seen in the detection toaster details), so look in the log: “c:\ProgramData\AVAST Software\Avast\report\WebShield.txt” where should be exact URL where it was found. If you think that it is false positive then fill-in this form: https://www.avast.com/false-positive-file-form.php, please.