pass options hash to octokit create_release 

- this is helpful when using travis to generate build artifacts and store them in a github release container but not marking it as a "final release".
- further optimizes the creation of the github release by setting some additional flags in `.travis.yml`:
- possible values ([method reference](http://octokit.github.io/octokit.rb/Octokit/Client/Releases.html#create_release-instance_method)):
  - target_commitish (String) — Specifies the commitish value that determines where the Git tag is created from.
  - name (String) — Name for the release
  - body (String) — Content for release notes
  - draft (String) — Mark this release as a draft
  - prerelease (String) — Mark this release as a pre-release
- full example:
```
deploy:
  provider: releases
  api-key: "GITHUB OAUTH TOKEN"

  target_commitish: "xxx"
  name: "custom-release"
  body: "custom release message"
  draft: false
  prerelease: true
```