powerdns DESC language adjustments

Hello,

the diff below changes DESCR-main of powerdns to correct a mishap and
uses "backend" without a dash, just as the first occurrence of the word.

Marcus

Index: pkg/DESCR-main
===================================================================
RCS file: /cvs/ports/net/powerdns/pkg/DESCR-main,v
retrieving revision 1.3
diff -u -p -u -r1.3 DESCR-main
--- pkg/DESCR-main 14 Apr 2015 18:10:27 -0000 1.3
+++ pkg/DESCR-main 30 Dec 2018 14:36:35 -0000
@@ -4,5 +4,5 @@ in nature. Additionally, through use of
PowerDNS offers very high domain resolution performance.

Backends for SQLite databases, BIND files and geographical load-balancing
-are including in the main package. MySQL, PostgreSQL and LDAP back-ends are
+are included in the main package. MySQL, PostgreSQL and LDAP backends are
packaged separately.