fix: issue when there's parameters in url

Hi,

When you're starting to use methods from the class Feedly with parameters (GET), the url used by your method InitCurl() isn't right.
Indeed, a '?' is missing when you're doing your concatenation.

For example: for the method getStreamContent('user/5e60ca13-09c3-4a4f-a735-b22204085d3c/category/news', ...)
the url used by InitCurl() is 
https://sandbox.feedly.com/v3/streams/contentsstreamId=user%2F5e60ca13-09c3-4a4f-a735-b22204085d3c%2Fcategory%2Fnews