fix: add user-agent header (#70)

Author: hakonharnes

lua/leetcode/api/headers.lua

@@ -7,6 +7,7 @@ function headers.get()
     local cookie = Cookie.get()
 
     return vim.tbl_extend("force", {
+        ["User-Agent"] = "Mozilla/5.0 (X11; Linux x86_64; rv:123.0) Gecko/20100101 Firefox/123.0",
         ["Referer"] = ("https://leetcode.%s"):format(config.domain),
         ["Origin"] = ("https://leetcode.%s/"):format(config.domain),
         ["Content-Type"] = "application/json",