gnu: openjpeg: Replace with 2.3.1 [security fixes].

This release includes many security fixes, including CVE-2018-5785 and
CVE-2018-CVE-2018-6616.  See
<https://github.com/uclouvain/openjpeg/blob/master/CHANGELOG.md> for details.

* gnu/packages/image.scm (openjpeg)[replacement]: New field.
(openjpeg-2.3.1): New public variable.

gnu/packages/image.scm

@@ -561,6 +561,7 @@ work.")
   (package
     (name "openjpeg")
     (version "2.3.0")
+    (replacement openjpeg-2.3.1)
     (source
       (origin
         (method url-fetch)
@@ -594,6 +595,20 @@ error-resilience, a Java-viewer for j2k-images, ...")
     (home-page "https://github.com/uclouvain/openjpeg")
     (license license:bsd-2)))
 
+(define-public openjpeg-2.3.1
+  (package
+    (inherit openjpeg)
+    (version "2.3.1")
+    (source (origin
+              (method git-fetch)
+              (uri (git-reference
+                    (url "https://github.com/uclouvain/openjpeg")
+                    (commit (string-append "v" version))))
+              (file-name (git-file-name "openjpeg" version))
+              (sha256
+               (base32
+                "1dn98d2dfa1lqyxxmab6rrcv52dyhjr4g7i4xf2w54fqsx14ynrb"))))))
+
 (define-public openjpeg-1
   (package (inherit openjpeg)
     (name "openjpeg")