feat(fun/uggc): create a rot13 url handler

Example usage:
$ /nix/store/9kgpv4n62vhxs971jkvwvvl3msm4wpm8-uggc/bin/uggc 'uggcf://gjvggre.pbz/alnabgrpu/fgnghf/1272363652679524352'

Change-Id: I8fd5f77416116ce1a6ab7f96d3f2c726ef663677
Reviewed-on: https://cl.tvl.fyi/c/depot/+/386
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: eta <eta@theta.eu.org>

fun/uggc/default.nix

@@ -0,0 +1,14 @@
+{ depot, ... }@args:
+
+let
+  gopkgs = depot.third_party.gopkgs;
+in
+depot.nix.buildGo.program {
+  name = "uggc";
+  srcs = [
+    ./main.go
+  ];
+  deps = [
+    gopkgs."github.com".pkg.browser.gopkg
+  ];
+}