updated shebang to use env (#67)

https://unix.stackexchange.com/questions/29608/why-is-it-better-to-use-usr-bin-env-name-instead-of-path-to-name-as-my

Author: gibatronic

README.md

@@ -934,7 +934,7 @@ nohup command &
 The first line that you will write in bash script files is called `shebang`. This line in any script determines the script's ability to be executed like a standalone executable without typing sh, bash, python, php etc beforehand in the terminal.
 
 ```bash
-#!/bin/bash
+#!/usr/bin/env bash
 ```
 
 ## 2.1. Variables