Update flake.nix for v0.51.0 (#637)

Updates flake.nix version to 0.51.0 for the v0.51.0 release.

Co-authored-by: Wes McKinney <wesm@users.noreply.github.com>

Author: wesm

flake.nix

@@ -15,7 +15,7 @@
         packages = {
           default = pkgs.buildGoModule {
             pname = "roborev";
-            version = "0.50.0";
+            version = "0.51.0";
 
             src = ./.;