Debian: Change `apt-get` to `apt`

Debian.md

@@ -12,8 +12,8 @@ All packages we provide are signed with the following [key](https://packages.ici
 Here’s how to add the official release repository:
 
 ```bash
-apt-get update
-apt-get -y install apt-transport-https wget gnupg
+apt update
+apt -y install apt-transport-https wget gnupg
 
 wget -O - https://packages.icinga.com/icinga.key | apt-key add -
 
@@ -23,7 +23,7 @@ DIST=$(awk -F"[)(]+" '/VERSION=/ {print $2}' /etc/os-release); \
  echo "deb-src https://packages.icinga.com/debian icinga-${DIST} main" >> \
  /etc/apt/sources.list.d/${DIST}-icinga.list
 
-apt-get update
+apt update
 ```
 
 ## Installing the Package
@@ -31,6 +31,6 @@ apt-get update
 Use your distribution's package manager to install the `<!-- {{ package }} -->` package as follows:
 
 ```bash
-apt-get install <!-- {{ package }} -->
+apt install <!-- {{ package }} -->
 ```
 <!-- {% include "02-Installation.md" %} -->