Import Debian changes 1.20.0-1

network-manager-l2tp (1.20.0-1) unstable; urgency=medium
.
  * New upstream release
  * Bump Standards-Version to 4.6.0
  * Fix capitalization error in package description
  * Update dependencies for NetworkManager >= 1.20.0
  * Remove redundant GPLv2/OpenSSL license conflict patch
  * Remove redundant intltool Build-Depends
  * Remove obsolete debian/network-manager-l2tp.maintscript
  * Drop override for dh_missing
    No longer needed with debhelper-compat 13