umurmur: move config file to its default location

umurmur: move config file to its default location

This was changed in version 0.3.1 [1]

Fixes initial start of umurmur:
```
root@turris:~# umurmurd
Error in config file /etc/umurmur/umurmur.conf line 0: file I/O error
```

And also while running help of umurmurd, the defailt location is /etc/umurmur/umurmur.conf
```
Usage: umurmurd [-d] [-r] [-h] [-p <pidfile>] [-t] [-c <conf file>] [-a <addr>] [-b <port>]
       -c <conf file> - Specify configuration file (default /etc/umurmur/umurmur.conf)
```
[1] https://github.com/umurmur/umurmur/commit/4f3ed41357bb6fcb7afddd5343b59cfef54d65a4

Fixes: c4a23ca99662e67c8b6f5b8bad76d93fc2381ea0 ("umurmur: update to version 0.3.1")
Signed-off-by: Josef Schlehofer <[email protected]>