gnu: maxflow: Correct version to 3.0.5.

This won't be picked up by ‘guix package -u’, but the code is identical
anyway.  By changing this now, fewer installations will fail to upgrade
at all if upstream ever release a new <3.4.

* gnu/packages/maths.scm (maxflow)[version]: Change to 3.0.5.
[source]: Use version tag instead of raw matching commit.

gnu/packages/maths.scm

@@ -1766,12 +1766,14 @@ (define-public gmsh
 (define-public maxflow
   (package
     (name "maxflow")
-    (version "3.04")
+    ;; Versioning is ambiguous: the git tag matching this commit is ‘3.0.5’,
+    ;; which matches CMakeLists.txt, but README.md and CHANGES say ‘3.04’.
+    (version "3.0.5")
     (source (origin
               (method git-fetch)
               (uri (git-reference
                     (url "https://github.com/gerddie/maxflow.git")
-                    (commit "42401fa54823d16b9da47716f04e5d9ef1605875")))
+                    (commit version)))
               (file-name (git-file-name name version))
               (sha256
                (base32