Use seq-position instead of string-search when setting hostname

Turns out string-search was only added pretty recently, so
seq-position is better in terms of portability (Debian still have an
old emacs in their repos, for example). Probably a tiny amount faster
too lol

config.org

@@ -62,9 +62,9 @@
 
    #+begin_src emacs-lisp
      (defun cut-at (delimeter string)
-       (substring string 0 (string-search delimeter string)))
+       (substring string 0 (seq-position string delimeter)))
 
-     (defvar hostname (cut-at "." (system-name)))
+     (defvar hostname (cut-at ?. (system-name)))
    #+end_src
 
 * Emacs Server