*: Use /usr/bin/env in shebangs for bash & zsh

To increase the portability (OSX for example has zsh under `/bin/zsh`).

.config/polybar/scripts/calendar.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # The separation and recursion is sadly necessary since reload is apparently
 # executed in a subshell and thus using an environment variable does not work