debian/copyright: Update based on upstream changes

No major changes, but a few minor ones.
diff --git a/debian/changelog b/debian/changelog
index f9f41ad..36d20d9 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -2,12 +2,12 @@
 
   * New upstream release.  Closes: #851615.
   * Drop patches; all were applied or otherwise fixed upstream.
+  * Update copyright file.
   * debian/control:
     - Use a stable repo.or.cz URL for packaging repo.
       Closes: #826382.  Thanks to Rolf Leggewie.
     - Use https for upstream homepage URL.
     - No longer Build-Depends: freebsd-glue on kfreebsd.
-  * copyright: Use https for upstream URLs.
   * get-orig-source: Use https for upstream Git repository.
   * liblzma:
     - Remove compatibility tricks that permit sharing a process with
diff --git a/debian/copyright b/debian/copyright
index 55c10c8..aac5b7a 100644
--- a/debian/copyright
+++ b/debian/copyright
@@ -78,7 +78,7 @@
  information.
 
 Files: *
-Copyright: 2006-2012, Lasse Collin
+Copyright: 2006-2018, Lasse Collin
            1999-2008, Igor Pavlov
            2006, Ville Koskinen
            1998, Steve Reid
@@ -114,7 +114,7 @@
 
 Files: INSTALL NEWS PACKAGERS
  windows/README-Windows.txt
- windows/INSTALL-Windows.txt
+ windows/INSTALL-MinGW.txt
 Copyright: 2009-2010, Lasse Collin
 License: probably-PD
  See the note on AUTHORS, README, and so on above.
@@ -156,6 +156,11 @@
 Copyright: © 2008, Steven G. Johnson <stevenj@alum.mit.edu>
 License: Autoconf
 
+files: m4/ax_check_capsicum.m4
+Copyright: © 2014, Google Inc.
+           © 2015, Lasse Collin <lasse.collin@tukaani.org>
+License: permissive-nowarranty
+
 Files: Doxyfile.in
 Copyright: © 1997-2007 by Dimitri van Heesch
 Origin: Doxygen 1.4.7