fix(script): fix typo of update_subscriptions.uc

[muink]

Running under vanilla Openwrt will produce the following error

root@Openwrt:~# /etc/homeproxy/scripts/update_subscriptions.uc
Syntax error: Invalid assignment to constant 'params'
In /etc/homeproxy/scripts/update_subscriptions.uc, line 276, byte 32:

 `            params = url.searchParams || {};`
  Near here -------------------------------^


Syntax error: Invalid assignment to constant 'params'
In /etc/homeproxy/scripts/update_subscriptions.uc, line 309, byte 32:

 `            params = url.searchParams || {};`
  Near here -------------------------------^


Syntax error: Invalid assignment to constant 'params'
In /etc/homeproxy/scripts/update_subscriptions.uc, line 336, byte 16:

 `            params = url.searchParams;`
  Near here ---------------^