Make write and close use await as well as per lib.

lib/devices/S7.ts

@@ -98,7 +98,7 @@ export class S7Connection extends DeviceConnection {
      * Writes metric values to the PLC
      * @param {array} metrics Array of metric objects to write to the PLC
      */
-    writeMetrics(metrics: Metrics) {
+    async writeMetrics(metrics: Metrics) {
         // This doesn't seem to work for Ixxx value writes
         // Untested with other writes at present
 
@@ -116,22 +116,22 @@ export class S7Connection extends DeviceConnection {
             // Notify user
             log(`Writing ${values} to ${addrs}`);
             // Write metric values
-            this.#itemGroup.writeItems(addrs, values);
+            await this.#itemGroup.writeItems(addrs, values);
         }
     }
 
     /**
      * Close connection and tidy up
      */
-    close() {
+    async close() {
         // Clear the variable list
         this.#vars = {};
         // Destroy the metric item group, if it exists
         if (this.#itemGroup) {
             this.#itemGroup.destroy();
         }
         // Close the PLC connection
-        this.#s7Conn.disconnect();
+        await this.#s7Conn.disconnect();
     }
 }