Fix a timing issue for sequential importLibrary calls

Works around googlemaps#809

Author: chrisjshull

src/index.ts

@@ -469,9 +469,11 @@ export class Loader {
     name: "visualization"
   ): Promise<google.maps.VisualizationLibrary>;
   public importLibrary(name: Library): Promise<unknown>;
-  public importLibrary(name: Library): Promise<unknown> {
+  public async importLibrary(name: Library): Promise<unknown> {
     this.execute();
-    return google.maps.importLibrary(name);
+    // Extra await here works around https://github.com/googlemaps/js-api-loader/issues/809. 
+    // This is kind of an icky timing workaround, but the issue really is that user code after importLibrary is getting invoked 1 microtask before the library code handles the completion. 
+    return await google.maps.importLibrary(name);
   }
 
   /**
@@ -629,7 +631,7 @@ export class Loader {
       // short circuit and warn if google.maps is already loaded
       if (window.google && window.google.maps && window.google.maps.version) {
         console.warn(
-          "Google Maps already loaded outside @googlemaps/js-api-loader." +
+          "Google Maps already loaded outside @googlemaps/js-api-loader. " +
             "This may result in undesirable behavior as options and script parameters may not match."
         );
         this.callback();