#!/usr/bin/env bash instead of #!/bin/bash in command line tool

[aleksmt]

Hello contributors of allure! There is a issue with shebang line in allure cli script located here https://github.com/allure-framework/allure-cli/blob/master/src/main/scripts/allure

I propose to use #!/usr/bin/env bash here, because in different systems bash location could be in another place (especially for FreeBSD) `[freebsd.local /bin]# which bash /usr/local/bin/bash

[freebsd.local /bin]# /bin/bash /bin/bash: Command not found.`

[vania-pooh]

Any PR is welcome. :)