Fixes some error messages

config/locales/en.yml

@@ -48,15 +48,15 @@ en:
         work_package:
           attributes:
             blocks_ids:
-              can_only_contain_work_packages_of_current_sprint: "can only contain the IDs of work packages in the current sprint"
-              must_block_at_least_one_work_package: "must contain the ID of at least one ticket"
+              can_only_contain_work_packages_of_current_sprint: "can only contain IDs of work packages in the current sprint."
+              must_block_at_least_one_work_package: "must contain the ID of at least one ticket."
             fixed_version_id:
-              task_version_must_be_the_same_as_story_version: "must be the same as the story's version"
+              task_version_must_be_the_same_as_story_version: "must be the same as the story's version."
             parent_id:
               parent_child_relationship_across_projects: "is invalid because the work package '%{work_package_name}' is a backlog task and therefore cannot have a parent outside of the current project."
-              type_must_be_one_of_the_following: "Type must be one of the following: %{type_names}"
+              type_must_be_one_of_the_following: "Type must be one of the following: %{type_names}."
         sprint:
-          cannot_end_before_it_starts: "Sprint cannot end before it starts"
+          cannot_end_before_it_starts: "Sprint cannot end before it starts."
 
   backlogs:
     add_new_story: "New Story"