man: Add a missing colon to separate a --force option

man/dpkg.1

@@ -535,7 +535,7 @@ it will be used to decide the final action.
 \fBoverwrite\fP:
 Overwrite one package's file with another's file.
 
-\fBoverwrite\-dir\fP
+\fBoverwrite\-dir\fP:
 Overwrite one package's directory with another's file.
 
 \fBoverwrite\-diverted\fP: