Allow disabling service incident timeouts

[pdecat]

Resolves #41

• add test case
• update vendored go-pagerduty once Remove omitempty json format options on service timeout fields heimweh/go-pagerduty#17 is merged

[pdecat]

Expected travis failure given the local vendor patch:

$ make vendor-status
The following packages are missing or modified locally:
	github.com/heimweh/go-pagerduty/pagerduty
Error: status failed for 1 package(s)
make: *** [vendor-status] Error 2
The command "make vendor-status" exited with 2.

[heimweh]

Hi @pdecat,

thanks for this PR.

This LGTM, as soon as the tests are green this should be good to go 👍

[pdecat]

Hi @heimweh, vendor updated, all green :)

[heimweh]

Hi @pdecat,

thank you so much for this. This LGTM 👍