Use secure copyright file specification URI.

Fixes lintian: insecure-copyright-format-uri
See https://lintian.debian.org/tags/insecure-copyright-format-uri.html for more details.

debian/changelog

@@ -1,3 +1,9 @@
+cmake (3.12.3-4) UNRELEASED; urgency=medium
+
+  * Use secure copyright file specification URI.
+
+ -- Jelmer Vernooij <jelmer@debian.org>  Sun, 28 Oct 2018 11:29:48 +0000
+
 cmake (3.12.3-3) unstable; urgency=medium
 
   * Fix info and man page install directories on kFreeBSD. (Closes: #911700)

debian/copyright

@@ -1,4 +1,4 @@
-Format: http://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
 Upstream-Name: cmake
 Source: http://www.cmake.org/files/v*/