Release to unstable.

debian/changelog

@@ -1,4 +1,4 @@
-cmake (3.12.3-1) UNRELEASED; urgency=medium
+cmake (3.12.3-1) unstable; urgency=medium
 
   * New upstream release.
     - Fixes FTBFS on hurd. (Closes: #900240)
@@ -6,7 +6,7 @@ cmake (3.12.3-1) UNRELEASED; urgency=medium
     - Fixes a test suite failure.
     - Cherry-pick upstream fix in hurd_so_noexec.patch
 
- -- Felix Geyer <fgeyer@debian.org>  Sun, 07 Oct 2018 12:57:42 +0200
+ -- Felix Geyer <fgeyer@debian.org>  Sun, 07 Oct 2018 16:38:46 +0200
 
 cmake (3.12.1-1.1) unstable; urgency=medium