fix #98 problem with p:create
Merge pull request #98 from cordoval/98-bug-when-not-using-source-org-and-source-branch-on-pr-command

This PR was merged into gushphp:master branch.

Discussion
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bug when not using --source-org and --source-branch on PR command

@Padam87 you did not check the command without arguments if it was still working

it is not working, can you please launch a PR fixing this? Thanks

```
  [Github\Exception\ValidationFailedException]
  Validation Failed: Field "head_sha" is missing, for resource "PullRequest", Field "base_sh
  a" is missing, for resource "PullRequest", No commits between gushphp:master and gushphp:8
  9-it-is-either-branch-push-or-b-fork-or-other-that-is-tracking-the-master-branch

```

Commits
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4ecc7bb95eb31ab2a0f3943bb6eb66ed3d70bd22 fix #98 problem with p:create cordoval