Fix import from gitlab.com

Fixes #12652

CHANGELOG

@@ -14,6 +14,7 @@ v 8.5.2
   - Fix sidebar overlapping content when screen width was below 1200px
   - Fix error 500 when commenting on a commit
   - Fix broken icons on installations with relative URL (Artem Sidorenko)
+  - Fix import from gitlab.com (KazSawada)
   - Fix help keyboard shortcut on relative URL setups (Artem Sidorenko)
 
 v 8.5.1

lib/gitlab/gitlab_import/importer.rb

@@ -12,7 +12,7 @@ module Gitlab
       end
 
       def execute
-        project_identifier = CGI.escape(project.import_source, '/')
+        project_identifier = CGI.escape(project.import_source)
 
         #Issues && Comments
         issues = client.issues(project_identifier)