Fix corrupted chars while reading from utf-8 stream

This issue was found during connecting Jira to Gerrit via Jira Gerrit
Plugin. Without charset (utf-8) specified, multi-byte chars could be
corrupted thus results in the JSON result returned from Gerrit cannot be
parsed at all.
Merge pull request #28 from jiangr/master

Fix corrupted chars while reading from utf-8 stream