completion/system: load earlier than other completions

I chose `325` so that it's still possible to deliberately place something *before* this component, if needed somehow.

completion/available/system.completion.bash

@@ -1,8 +1,11 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 #
 # Loads the system's Bash completion modules.
 # If Homebrew is installed (OS X), it's Bash completion modules are loaded.
 
+# Load before other completions
+# BASH_IT_LOAD_PRIORITY: 325
+
 if shopt -qo nounset
 then # Bash-completion is too large and complex to expect to handle unbound variables throughout the whole codebase.
 	__bash_it_restore_nounset=true