v1.7.4

@appleboy:
73aca36 add ARCHS variable.
e5b916c fix: GOMAXPROCS set to the number of cores available in 1.5
015a23d feat: add new flag --pid
d8c4659 feat: creat pid folder automatically.
9f87268 fix: Clone tags within drone for proper version generation
cbbbc4e fix: Enforce custom LDFLAGS within makefile and add coverage command.
a669070 feat: support prometheus metric url. (#168)
9bd6886 refactor: Support empty notification for android (#170)
2a00ed7 feat: support title flag on cli (#172)