fix StaticHandler process http ranges header bug

[fznply]

support ranges as below:
Range: bytes=0-499 // from 0 to 499, total 500 bytes
Range: bytes=-500 // the last 500 bytes
Range: bytes=500- // from 500th to the last, include the last byte
Range: bytes=500-500 // the 500th, total 1 byte

fix end_pos
Content-Range: bytes {start_pos}-{end_pos}/{total_length} // end_pos <= total_length -1

[danieldaeschle]

https://circleci.com/gh/vibora-io/vibora/225?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

Please fix your code style issue.