admins: fix import course member

Gemfile.lock

@@ -423,4 +423,4 @@ RUBY VERSION
    ruby 2.3.7p456
 
 BUNDLED WITH
-   2.0.2
+   1.17.3

app/services/admins/import_course_member_service.rb

@@ -36,7 +36,7 @@ class Admins::ImportCourseMemberService < ApplicationService
 
     member = course.course_members.find_by(user_id: user.id, role: data.role.to_i)
     # 如果已是课堂成员且是学生身份and不在指定的分班则移动到该分班
-    if member.present? && member.role == :STUDENT && course_group && member.course_group_id != course_group&.id
+    if member.present? && member.role == 'STUDENT' && course_group && member.course_group_id != course_group&.id
       member.update!(course_group_id: course_group&.id)
     elsif member.blank?
       course.course_members.create!(user_id: user.id, role: data.role.to_i, course_group_id: course_group&.id)