Properly resolve SHA for PRs

tools/gulp/tasks/payload.ts

@@ -33,15 +33,15 @@ task('payload', ['material:clean-build'], async () => {
   if (isTravisBuild()) {
     // Open a connection to Firebase. For master builds the database will use an admin account.
     const database = openFirebaseDashboardDatabase(isTravisMasterBuild());
-    const currentSha = process.env['TRAVIS_COMMIT'];
+    const currentSha = process.env['TRAVIS_PULL_REQUEST_SHA'] || process.env['TRAVIS_COMMIT'];
     const previousPayload = await getLastPayloadResults(database);
 
     // Calculate library sizes by combining the CDK and Material FESM 2015 bundles.
     const previousSize = previousPayload.cdk_fesm_2015 + previousPayload.material_fesm_2015;
     const currentSize = results.cdk_fesm_2015 + results.material_fesm_2015;
     const deltaSize = currentSize - previousSize;
 
-    setGithubStatus(process.env['TRAVIS_COMMIT'], {
+    await setGithubStatus(process.env['TRAVIS_COMMIT'], {
       result: true,
       name: 'Library Payload',
       url: `https://travis-ci.org/angular/material2/jobs/${process.env['TRAVIS_JOB_ID']}`,