clean apt commands

update/upgrade command are not necessary and can also be assumed to be sufficiently up to date

Author: mwarning

README.md

@@ -12,9 +12,8 @@ To build the firmware yourself you need a Unix console to enter commands into.
 Install dependencies for the build environment (Debian/Ubuntu):
 
 ```bash
-    sudo apt-get update; sudo apt-get upgrade
-    sudo apt-get install subversion g++ zlib1g-dev build-essential git python
-    sudo apt-get install libncurses5-dev gawk gettext unzip file libssl-dev wget
+    sudo apt install subversion g++ zlib1g-dev build-essential git python
+    sudo apt install libncurses5-dev gawk gettext unzip file libssl-dev wget
 ```
 Build commands for the console: