Fix has_gnu_parallel function

Different distributions package the parallel command in ways that
generate differing output from --version.  Adjust the grep to look
'gnu parallel' case insensitive to account for these differences.

Reported-by: Genes Lists <lists@sapience.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

copy-firmware.sh

@@ -22,7 +22,7 @@ warn() {
 
 has_gnu_parallel() {
     if command -v parallel > /dev/null; then
-        if parallel --version | grep -Fq 'GNU Parallel'; then
+        if parallel --version | grep -Fqi 'gnu parallel'; then
            return 0
         fi
     fi