allow overriding the http request scheme

[amsoell]

Added a simple way to override the default "scheme" property of the http request. When using apac in a desktop application such as Electron, all http requests are attempted with the 'file://" scheme by default—this provides a way to force the requests to go through via http or https

[dmcquay]

Thanks for your contribution. This looks great except that it is lacking tests. Please update operation-helper.specs.js to cover this case.

[dmcquay]

Awesome, thanks for following through. Reviewing...

[dmcquay]

You are testing that the option is passed in and set on the operation helper, but you are not testing that the scheme is passed into the http options. At minimum, I suggest you add the scheme option to the existing happy path test here: https://github.com/MettleUp/node-apac/blob/010f78f0b410e845c547ac5b0aea9cd2077ed7b0/lib/operation-helper.specs.js#L161 and assert that it was passed into the http requests around here: https://github.com/MettleUp/node-apac/blob/010f78f0b410e845c547ac5b0aea9cd2077ed7b0/lib/operation-helper.specs.js#L191

[amsoell]

Sorry, my JS testing chops are a little dusty— let me know if there's anything else you suggest here.

[dmcquay]

Looks great! Thanks @amsoell.