[IMP] pr_template: match template with commit format

With the introduction of npm releases we decided to put the relation to
the odoo task with the format "Task: xxxxx". This changes the PR template
to match this format.

closes #2668

X-original-commit: c9e6ec9
Signed-off-by: Lucas Lefèvre (lul) <lul@odoo.com>

.github/pull_request_template.md

@@ -2,7 +2,7 @@
 
 description of this task, what is implemented and why it is implemented that way.
 
-Odoo task ID : [TASK_ID](https://www.odoo.com/web#id=TASK_ID&action=333&active_id=2328&model=project.task&view_type=form&cids=1&menu_id=4720)
+Task: : [TASK_ID](https://www.odoo.com/web#id=TASK_ID&action=333&active_id=2328&model=project.task&view_type=form&cids=1&menu_id=4720)
 
 ## review checklist