Encoding::InvalidByteSequenceError

# Report

## What did you do?

Run `bundle exec danger`

## What did you expect to happen?

Running swiftlint and comment on PR on BitBucket Server (Stash)

## What happened instead?

```
bundler: failed to load command: danger (/Users/jenkins/.rbenv/versions/2.3.1/bin/danger)
Encoding::InvalidByteSequenceError: "\xE2" on US-ASCII
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/request_sources/bitbucket_server_api.rb:51:in `encode'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/request_sources/bitbucket_server_api.rb:51:in `to_json'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/request_sources/bitbucket_server_api.rb:51:in `post_comment'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/request_sources/bitbucket_server.rb:80:in `update_pull_request!'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/danger_core/dangerfile.rb:247:in `post_results'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/danger_core/dangerfile.rb:277:in `run'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/danger_core/executor.rb:27:in `run'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/lib/danger/commands/runner.rb:66:in `run'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/claide-1.0.1/lib/claide/command.rb:334:in `run'
/Users/jenkins/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/danger-5.2.2/bin/danger:5:in `'
/Users/jenkins/.rbenv/versions/2.3.1/bin/danger:23:in `load'
/Users/jenkins/.rbenv/versions/2.3.1/bin/danger:23:in `'
Build step 'Execute shell' marked build as failure
```

## Your Environment

* Which CI are you running on? Jenkins ver. 2.62
* Are you running the latest version of Danger? yes, 5.2.2
* Atlassian Bitbucket v4.13.0
* What is your Dangerfile?

```ruby
message("Hello, this worked")

swiftlint.lint_files
wiftlint.lint_files inline_mode: true
```