Change sync call to HyperLedger to async

[juniwang]

see https://github.com/kaiyuanshe/kcoin/blob/master/src/web/helpers/github_helpers.rb#L83, we call server api synchronously, we'd better change it async mode.

Please:

• introduce ruby library rufus
• As a first example, change https://github.com/kaiyuanshe/kcoin/blob/master/src/web/helpers/github_helpers.rb#L83 to asynchronous mode
• Better create a new async module for commonly, so that we can easily adopt across the kcoin project