fix(github): handle ‘empty’ repository properly

lib/workers/repository/error.js

@@ -13,6 +13,11 @@ async function handleError(config, err) {
     delete config.branchList; // eslint-disable-line no-param-reassign
     return err.message;
   }
+  if (err.message === 'empty') {
+    logger.info('Repository is empty - skipping');
+    delete config.branchList; // eslint-disable-line no-param-reassign
+    return err.message;
+  }
   if (err.message === 'disabled') {
     logger.info('Repository is disabled - skipping');
     return err.message;

test/workers/repository/error.spec.js

@@ -12,6 +12,7 @@ describe('workers/repository/error', () => {
   describe('handleError()', () => {
     const errors = [
       'uninitiated',
+      'empty',
       'disabled',
       'repository-changed',
       'fork',