Update to latest Zephyr and their Docker repo

src/util.c

@@ -102,6 +102,8 @@ uint64_t mg_millis(void) {
   return xTaskGetTickCount() * portTICK_PERIOD_MS;
 #elif MG_ARCH == MG_ARCH_AZURERTOS
   return tx_time_get() * (1000 /* MS per SEC */ / TX_TIMER_TICKS_PER_SECOND);
+#elif MG_ARCH == MG_ARCH_ZEPHYR
+  return (uint64_t) k_uptime_get();
 #elif MG_ARCH == MG_ARCH_UNIX && defined(__APPLE__)
   // Apple CLOCK_MONOTONIC_RAW is equivalent to CLOCK_BOOTTIME on linux
   // Apple CLOCK_UPTIME_RAW is equivalent to CLOCK_MONOTONIC_RAW on linux
@@ -128,3 +130,4 @@ uint64_t mg_millis(void) {
 #endif
 }
 #endif
+