logs: log latest commit time

lib/platform/git/storage.js

@@ -113,6 +113,12 @@ class Storage {
           ) / 10;
         logger.info({ cloneSeconds }, 'git clone completed');
       }
+      try {
+        const latestCommitDate = (await git.log({ n: 1 })).latest.date;
+        logger.debug({ latestCommitDate }, 'latest commit');
+      } catch (err) /* istanbul ignore next */ {
+        logger.warn({ err }, 'Cannot retrieve latest commit date');
+      }
 
       if (global.gitAuthor) {
         logger.info({ gitAuthor: global.gitAuthor }, 'Setting git author');