Add missing libnm-gtk Require and BuildRequire

for
d291de3 auth-dialog: port to libnm-gtk's NMAVpnPasswordDialog

NetworkManager-pptp.spec

@@ -19,6 +19,7 @@ BuildRequires: glib2-devel
 BuildRequires: ppp-devel
 BuildRequires: libtool intltool gettext
 BuildRequires: libsecret-devel
+BuildRequires: libnm-gtk-devel
 
 Requires: gtk3
 Requires: dbus
@@ -27,6 +28,7 @@ Requires: pptp
 Requires: ppp
 Requires: shared-mime-info
 Requires: gnome-keyring
+Requires: libnm-gtk
 Obsoletes: NetworkManager-pptp < 1:0.9.8.2-3
 
 %global _privatelibs libnm-pptp-properties[.]so.*