Remove failing chmod call

This call leads to the error on `git clone`:
> Worker: RepositoryFetchingWorker
> Arguments: 1, "clone", "fork"
> Error: Errno::EPERM: Operation not permitted @ chmod_internal - /data/git/repositories/1/

Instead, we should set the umask correctly:
umask 002

lib/git_repository.rb

@@ -24,14 +24,9 @@ def initialize(path)
     else
       FileUtils.mkdir_p(Ontohub::Application.config.git_root)
       @repo = Rugged::Repository.init_at(path, true)
-      set_group_permissions
     end
   end
 
-  def set_group_permissions
-    FileUtils.chmod_R('g+ws', path)
-  end
-
   def destroy
     FileUtils.rmtree(self.path)
   end

lib/git_repository/cloning.rb

@@ -12,9 +12,7 @@ def clone(url)
       fetch:  '+refs/*:refs/*',
       mirror: 'true'
 
-    result = pull
-    set_group_permissions
-    result
+    pull
   end
 
   def clone_svn(url)
@@ -32,9 +30,7 @@ def clone_svn(url)
     end
 
     set_section %w(svn-remote svn), options
-    result = pull_svn
-    set_group_permissions
-    result
+    pull_svn
   end
 
   def pull