igmp proxy: tweak names suggested by @fabianfrz

src/opnsense/mvc/app/models/OPNsense/IGMPProxy/ACL/ACL.xml

 <acl>
     <page-services-igmpproxy>
-        <name>Services: Igmpproxy</name>
+        <name>Services: IGMP Proxy</name>
         <patterns>
             <pattern>services_igmpproxy.php*</pattern>
         </patterns>
     </page-services-igmpproxy>
     <page-services-igmpproxy-edit>
-        <name>Services: Igmpproxy: Edit</name>
+        <name>Services: IGMP Proxy: Edit</name>
         <patterns>
             <pattern>services_igmpproxy_edit.php*</pattern>
         </patterns>