Add apt-get update to contributing guide.
This allows apt-get to work correctly even if the base container is a bit out of date.
<execute-list host="{[host-contrib]}">
<title>Install development tools</title>
+ <execute user="root" pre="y" show="n">
+ <exe-cmd>
+ apt-get update
+ </exe-cmd>
+ </execute>
+
<execute user="root" pre="y">
<exe-cmd>
apt-get install rsync git devscripts build-essential valgrind lcov autoconf
