more refactoring - easier guessing path changes

lib/gitlab/import_export/project_tree_saver.rb

@@ -25,7 +25,7 @@ module Gitlab
       end
 
       def project_filename
-        "#{@project.name}.json"
+        "project.json"
       end
 
       def project_json_tree

lib/gitlab/import_export/repo_bundler.rb

@@ -27,7 +27,7 @@ module Gitlab
       end
 
       def project_filename
-        "#{@project.name}.bundle"
+        "project.bundle"
       end
 
       def path_to_repo

lib/gitlab/import_export/wiki_repo_bundler.rb

@@ -19,7 +19,7 @@ module Gitlab
       private
 
       def project_filename
-        "#{@project.name}.wiki.bundle"
+        "project.wiki.bundle"
       end
 
       def path_to_repo