fsspec: fixing build and dependencies

[juarezr]

This PR has the objective of fixing the build that is not working.

The problem is registered in this issue

Changes

1. Added package aiohttp to optional_requirements.txt
2. Added a http optional dependecy in extra_requires in setup.py

Checklist

Checklist for for pull requests including new code and/or changes to existing code...

• Code
  • Includes unit tests
  • All changes documented in docs/changes.rst
• Testing
  • (Optional) Tested local against remote servers
  • Travis CI passes (unit tests run under Linux)
  • AppVeyor CI passes (unit tests run under Windows)
  • Unit test coverage has not decreased (see Coveralls)
• Changes
  • Ready to review
  • Ready to merge

[coveralls]

Coverage remained the same at 91.912% when pulling 4e2ddcd on juarezr:fix_aiohttp into 9ae3fc4 on petl-developers:master.

[juarezr]

Proceeding with the merge because:

• There are no code changes in python public API.
• There is no change in behavior for petl
• This fixes the travis-CI build for the other PR like Allow reading and writing Excel files in remote sources #506 and # 507