Fix git bundle test re: main branch

Author: mislav

features/steps.rb

@@ -61,7 +61,7 @@
 
   Dir.mktmpdir do |tmpdir|
     Dir.chdir(tmpdir) do
-      `git init --quiet`
+      `git -c init.defaultBranch=master init --quiet`
       `GIT_COMMITTER_NAME=a GIT_COMMITTER_EMAIL=b git commit --quiet -m 'empty' --allow-empty --author='a <b>'`
       `git bundle create "#{dest}" master 2>&1`
     end