Fix typo on en language locale file

Author: lunny

options/locale/locale_en-US.ini

@@ -1551,7 +1551,7 @@ issues.filter_project = Project
 issues.filter_project_all = All projects
 issues.filter_project_none = No project
 issues.filter_assignee = Assignee
-issues.filter_assginee_no_assignee = Assigned to nobody
+issues.filter_assignee_no_assignee = Assigned to nobody
 issues.filter_assignee_any_assignee = Assigned to anybody
 issues.filter_poster = Author
 issues.filter_user_placeholder = Search users