Fixes agnoster and barbuk theme .bash headers

themes/agnoster/agnoster.theme.bash

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 # vim: ft=bash ts=2 sw=2 sts=2
 #
 # agnoster's Theme - https://gist.github.com/3712874

themes/barbuk/barbuk.theme.bash

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 # shellcheck disable=2034,2154
 
 # Theme custom glyphs