[Multiple issue asignees] fix importers and specs for them

lib/gitlab/fogbugz_import/importer.rb

@@ -122,15 +122,15 @@ module Gitlab
           author_id = user_info(bug['ixPersonOpenedBy'])[:gitlab_id] || project.creator_id
 
           issue = Issue.create!(
-            iid:         bug['ixBug'],
-            project_id:  project.id,
-            title:       bug['sTitle'],
-            description: body,
-            author_id:   author_id,
-            assignee_id: assignee_id,
-            state:       bug['fOpen'] == 'true' ? 'opened' : 'closed',
-            created_at:  date,
-            updated_at:  DateTime.parse(bug['dtLastUpdated'])
+            iid:          bug['ixBug'],
+            project_id:   project.id,
+            title:        bug['sTitle'],
+            description:  body,
+            author_id:    author_id,
+            assignee_ids: [assignee_id],
+            state:        bug['fOpen'] == 'true' ? 'opened' : 'closed',
+            created_at:   date,
+            updated_at:   DateTime.parse(bug['dtLastUpdated'])
           )
 
           issue_labels = ::LabelsFinder.new(nil, project_id: project.id, title: labels).execute(skip_authorization: true)

lib/gitlab/github_import/issue_formatter.rb

@@ -10,7 +10,7 @@ module Gitlab
           description: description,
           state: state,
           author_id: author_id,
-          assignee_id: assignee_id,
+          assignee_ids: [assignee_id],
           created_at: raw_data.created_at,
           updated_at: raw_data.updated_at
         }

lib/gitlab/google_code_import/importer.rb

@@ -92,13 +92,13 @@ module Gitlab
           end
 
           issue = Issue.create!(
-            iid:         raw_issue['id'],
-            project_id:  project.id,
-            title:       raw_issue['title'],
-            description: body,
-            author_id:   project.creator_id,
-            assignee_id: assignee_id,
-            state:       raw_issue['state'] == 'closed' ? 'closed' : 'opened'
+            iid:          raw_issue['id'],
+            project_id:   project.id,
+            title:        raw_issue['title'],
+            description:  body,
+            author_id:    project.creator_id,
+            assignee_ids: [assignee_id],
+            state:        raw_issue['state'] == 'closed' ? 'closed' : 'opened'
           )
 
           issue_labels = ::LabelsFinder.new(nil, project_id: project.id, title: labels).execute(skip_authorization: true)

spec/lib/gitlab/google_code_import/importer_spec.rb

@@ -49,7 +49,7 @@ describe Gitlab::GoogleCodeImport::Importer, lib: true do
       expect(issue).not_to be_nil
       expect(issue.iid).to eq(169)
       expect(issue.author).to eq(project.creator)
-      expect(issue.assignee).to eq(mapped_user)
+      expect(issue.assignees).to eq([mapped_user])
       expect(issue.state).to eq("closed")
       expect(issue.label_names).to include("Priority: Medium")
       expect(issue.label_names).to include("Status: Fixed")