Fixes brokenness in the gemspec
Fixes brokenness in the gemspec

* Removes the hard-coded date. Rubygems will automatically fill this
field with the current date when you build the gem, definitely what we
want.
* Shortens the description down to two sentences. If people want full
usage examples they'll go to the README.
* Uses the the license option of the gemspec.

aareano/shopify_api,DanielVartanov/shopify_api,Shopify/shopify_api,cefigueiredo/shopify_api,kevinmpowell/shopify_api,resistorsoftware/shopify_api,discolabs/shopify_api,ipmobiletech/shopify_api,carsonreinke/shopify_api,kingscott/shopify_api,lalithr95/shopify_api