refactor(l10n): parse datetime with built-in function

Simplify date parsing. The date value is converted to ISO8601-like
format in UTC (Z) and parsed using built-in Date.parse().

locust/templates/report.html

@@ -225,13 +225,7 @@ <h2>Charts</h2>
                 return currentContent;
             }
 
-            let [date, time] = currentContent.split(" ");
-            let utcDateTime = new Date();
-            let [year, month, day] = date.split("-")
-            utcDateTime.setUTCFullYear(year, parseInt(month) - 1, day);
-            utcDateTime.setUTCHours(...(time.split(":")));
-
-            return utcDateTime.toLocaleString();
+            return new Date(Date.parse(currentContent.replace(" ", "T") + ".000Z")).toLocaleString();
         });
     </script>
 </body>