Fix LDAP authentication for Git HTTP access

CHANGELOG

 v 7.5.0
   - API: Add support for Hipchat (Kevin Houdebert)
   - Add time zone configuration on gitlab.yml (Sullivan Senechal)
+  - Fix LDAP authentication for Git HTTP access
 v 7.4.0
   - Refactored membership logic

lib/gitlab/ldap/authentication.rb

@@ -42,7 +42,7 @@ module Gitlab
       end
       def adapter
-        OmniAuth::LDAP::Adaptor.new(config.options)
+        OmniAuth::LDAP::Adaptor.new(config.options.symbolize_keys)
       end
       def config
@@ -68,4 +68,4 @@ module Gitlab
       end
     end
   end
-end
\ No newline at end of file
+end