Fix broken mem in prosody 0.10.2-1

[theatischbein]

The prosody mem output seems to be changed or not working anymore. Fixed now.

Sampe Output:

| ____ \ / _
| _ \ _ __ ___ ___ - | | _
| |_) | '/ _ / |/ _ \ / ` | | | | | __/| | | () _ \ || | (| | || | || |_| _/|/_/ _,|_, | A study in simplicity |___/

| Welcome to the Prosody administration console. For a list of commands, type: help | You may find more help on using this console in our online documentation at
| http://prosody.im/doc/console

| Process: 46.30MB | Used: 45.69MB (30.27MB by Lua) | Free: 105.77KB (105.56KB returnable) | OK: OK

Updatet mem telnet command to server:memory() and fixed broken reg match.

[t2d]

@JonnyTischbein Your PR doesn't work for me. The patch from https://github.com/jarus/munin-prosody/issues/8#issuecomment-282483976 does. Also, the indentation is broken.

EDIT: prosody 0.11.0