Update agent string: the selected string is the most abundant one on 06 Dec 2018 with a percentage of almost 10%

Signed-off-by: DL6ER <dl6er@dl6er.de>

gravity.sh

@@ -206,7 +206,7 @@ gravity_SetDownloadOptions() {
     activeDomains[$i]="${saveLocation}"
 
     # Default user-agent (for Cloudflare's Browser Integrity Check: https://support.cloudflare.com/hc/en-us/articles/200170086-What-does-the-Browser-Integrity-Check-do-)
-    agent="Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2227.0 Safari/537.36"
+    agent="Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36"
 
     # Provide special commands for blocklists which may need them
     case "${domain}" in