fix(project): queue spinner promises on watch

fixes #19
- on fast rebuilds, the change event would be fired quickly enough that
it would cause the spinner to succeed before it could be started
completely. This ensures the succeed call happens after the start call.
It also fixes the timer

Author: acburdine

src/project.ts

@@ -237,16 +237,21 @@ export default class Project {
       addonProject.watch({ onBuild: options.onBuild, outputDir: addonDist });
     });
 
+    let startPromise: Promise<void>;
+
     // Handle watcher events
     watcher.on('buildstart', async () => {
       debug('changes detected, rebuilding');
-      await spinner.start(`Building ${ this.pkg.name }`);
       timer = startTimer();
+      startPromise = spinner.start(`Building ${ this.pkg.name }`);
+      await startPromise;
     });
     watcher.on('change', async (results: { directory: string, graph: any }) => {
       debug('rebuild finished, wrapping up');
       this.finishBuild(results, options.outputDir);
+      await startPromise;
       await spinner.succeed(`${ this.pkg.name } build complete (${ timer.stop() }s)`);
+      startPromise = null;
       options.onBuild(this);
     });
     watcher.on('error', async (error: any) => {