Fix shellchecker header script to consider multiple lines

The shellcheck directive can appear after the shebang line, but the
script was only considering the first line.

hooks/dot-bash.sh

@@ -11,8 +11,8 @@ for file in "$@"; do
 
 	# Confirm expected schellcheck header
 	#
-	LINE1="$(head -n 1 "${file}")"
-	if [[ "${LINE1}" != "# shellcheck shell=bash" ]]; then
+	HEADER="$(head -n 2 "${file}")"
+	if [[ "${HEADER}" != *"# shellcheck shell=bash"* ]]; then
 		echo "Bash include file \`${file}\` has bad/missing shellcheck header"
 		exit_code=1
 	fi

themes/base.theme.bash

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# shellcheck shell=bash
 
 CLOCK_CHAR_THEME_PROMPT_PREFIX=''
 CLOCK_CHAR_THEME_PROMPT_SUFFIX=''