[Koha] Koha upgrade from 17.11 to 18.05

[Father Vlasie]

Hello everyone,

I am new to this mailing list. I am the IT person for 
the St. Photios Orthodox Theological Seminary in
Etna, California, U.S.A.

I have been working on and off with Koha for about
a year. We are finally getting close to cataloguing
our library.

I am very excited for the new 18.05 release but when 
I try to upgrade through my Debian (4.9.0-6-amd64 
#1 SMP Debian 4.9.82-1+deb9u3 (2018-03-02)) system
I get the following feedback:

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root at owl:# apt-get update
Get:1 http://security.debian.org stretch/updates InRelease [94.3 kB]
Get:2 http://security.debian.org stretch/updates/main Sources [140 kB]
Get:3 http://security.debian.org stretch/updates/main amd64 Packages [353 kB]
Ign:4 http://deb.debian.org/debian stretch InRelease
Get:5 http://deb.debian.org/debian stretch-updates InRelease [91.0 kB]                                         
Hit:6 http://deb.debian.org/debian stretch Release                                                                    
Get:8 http://security.debian.org stretch/updates/main Translation-en [165 kB]                                      
Get:9 http://debian.koha-community.org/koha stable InRelease [4,566 B]
Get:10 http://debian.koha-community.org/koha stable/main amd64 Packages [18.8 kB]
Fetched 867 kB in 1s (519 kB/s) 
Reading package lists... Done
W: Conflicting distribution: http://debian.koha-community.org/koha stable InRelease (expected 17.11 but got 18.05)

----

If I try to upgrade anyway it holds koha-common back:

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root at owl:# apt-get upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  koha-common libmoo-perl
The following packages will be upgraded:
  libprocps6 procps
2 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

----

Any help would be much appreciated!

Sincerely,

Father Vlasie

St. Photios Orthodox Theological Seminary
510 Collier Way, Etna, CA 96027, U.S.A.
www.spots.school