Improve default subject template
Improve default subject template

GoogleCloudPlatform/alertmanager,sarathsp06/alertmanager,ericgerling/alertmanager,tinytub/alertmanager,novilabs/alertmanager,Aloomaio/alertmanager,tyrken/alertmanager,prometheus/alertmanager,tbouvet/alertmanager,MonsantoCo/alertmanager,tyrken/alertmanager,Kellel/alertmanager,brancz/alertmanager,joehandzik/alertmanager,tbouvet/alertmanager,Kellel/alertmanager,sarathsp06/alertmanager,Aloomaio/alertmanager,prometheus/alertmanager,brancz/alertmanager,novilabs/alertmanager,ericgerling/alertmanager,novilabs/alertmanager,tyrken/alertmanager,MonsantoCo/alertmanager,pdf/alertmanager,pdf/alertmanager,GoogleCloudPlatform/alertmanager,novilabs/alertmanager,brancz/alertmanager,prometheus/alertmanager,tbouvet/alertmanager,brunoqc/alertmanager,MonsantoCo/alertmanager,brunoqc/alertmanager,joehandzik/alertmanager,Aloomaio/alertmanager,GoogleCloudPlatform/alertmanager,tinytub/alertmanager,brancz/alertmanager,prometheus/alertmanager,tinytub/alertmanager,sarathsp06/alertmanager,tyrken/alertmanager,pdf/alertmanager,Kellel/alertmanager,brunoqc/alertmanager,MonsantoCo/alertmanager,pdf/alertmanager,GoogleCloudPlatform/alertmanager,joehandzik/alertmanager,ericgerling/alertmanager,brunoqc/alertmanager