*.sh: POSIX compliance when needed

thirdparty/fetch-geoip-db.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 # Die on any error for Travis CI to automatically retry:
 set -e
@@ -10,7 +10,7 @@ cd "${download_dir}"
 filename="GeoLite2-Country.mmdb.gz"
 
 # Database does not exist or is older than 30 days.
-if [[ ! -e $filename ]] || [[ -n $(find . -name $filename -mtime +30 -print) ]]; then
+if [ ! -e $filename ] || [ -n "$(find . -name $filename -mtime +30 -print)" ]; then
 	rm -f $filename
 	echo "Updating GeoIP country database from MaxMind."
 	curl -s -L -O http://geolite.maxmind.com/download/geoip/database/$filename