[mobile-broadband-provider-info] dtd: expand DTD to include information for vvm3 Visual Voicemail standard

[Lubomir Rintel <lkundrak src gnome org>]

commit fe3ea72ecaa3eb5f0827c7373c90bc65b942ab6d
Author: Chris Talbot <chris talbothome com>
Date:   Mon Mar 14 18:06:56 2022 +0000

    dtd: expand DTD to include information for vvm3 Visual Voicemail standard
    
    This commit expands the DTD to include the vvm3 standard for visual voicemail.
    
    vvm3 is a standard that Verizon Wireless in the USA uses.
    
    https://gitlab.gnome.org/GNOME/mobile-broadband-provider-info/-/merge_requests/63

 serviceproviders.2.dtd | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/serviceproviders.2.dtd b/serviceproviders.2.dtd
index 8f87ed8..5bba12a 100644
--- a/serviceproviders.2.dtd
+++ b/serviceproviders.2.dtd
@@ -37,8 +37,8 @@
                             carrier-prefix?)>
 
 <!ELEMENT standard EMPTY>
-<!ATTLIST standard type (cvvm|otmp|proprietary) #REQUIRED>
-<!-- Whether the carrier supports OTMP or CVVM for Visual Voicemail
+<!ATTLIST standard type (cvvm|otmp|vvm3|proprietary) #REQUIRED>
+<!-- Whether the carrier supports OTMP, CVVM, or VVM3 for Visual Voicemail
      Some carriers implement their own proprietary standard.
 -->