Set proper locale inside nix-shell

This should prevent error:

  Failed to configure LOCALE for invalid locale name.

which prevented redis-server from starting, hence no redis.pid or
redis.sock files present.

support/nix/redis.nix

@@ -1,11 +1,15 @@
 with import <nixpkgs> {};
 
 mkShell {
-  buildInputs = [ redis ];
+  buildInputs = [ redis glibcLocales ];
 
   shellHook = ''
     ${builtins.readFile ./pushtrap.sh}
 
+    LOCALE_ARCHIVE = "${glibcLocales}/lib/locale/locale-archive"
+    LANG = "en_US.UTF-8"
+    LC_ALL = "en_US.UTF-8"
+
     TMP=$(mktemp -d)
     SOCKET=$TMP/redis.sock
     PIDFILE=$TMP/redis.pid