Print the PR Link
Print the PR Link if successful.

**Before:**
```bash
juan@x ~/code/ master|✓ [1]$ nimble publish
      Info: Using GitHub API Token in file: /home/juan/.nimble/github_api_token
   Success: Verified as juancarlospaco
    Copying packages fork into: /tmp/nimble-packages-fork
   Updating the fork
    Prompt: Whitespace separated list of tags?
    Answer: foo bar
    Pushing to remote of fork.
       Info Creating PR
   Success: Pull request successful.
juan@x ~/code/ master|✓ $
```

**After:**
```bash
juan@x ~/code/ master|✓ [1]$ nimble publish
      Info: Using GitHub API Token in file: /home/juan/.nimble/github_api_token
   Success: Verified as juancarlospaco
    Copying packages fork into: /tmp/nimble-packages-fork
   Updating the fork
    Prompt: Whitespace separated list of tags?
    Answer: foo bar
    Pushing to remote of fork.
       Info Creating PR
   Success: Pull request successful at https://github.com/nim-lang/packages/pull/666
juan@x ~/code/ master|✓ $
```