Simple fix for use of different timedate format in users endpoint

[MJRLegends]

Fix the following error, seems https://mixer.com/api/v1/users ISO 8601 format for timedate got changed

Caused by: com.google.gson.JsonSyntaxException: java.io.IOException: mixer: unable to parse date (2015-03-18T22:46:16+00:00)
    at com.google.gson.Gson.fromJson(Gson.java:818)
    at com.google.gson.Gson.fromJson(Gson.java:768)
    at com.google.gson.Gson.fromJson(Gson.java:717)
    at com.google.gson.Gson.fromJson(Gson.java:689)
    at com.mixer.api.http.MixerHttpClient.handleResponse(MixerHttpClient.java:239)
    at com.mixer.api.http.MixerHttpClient.handleRequest(MixerHttpClient.java:218)
    at com.mixer.api.http.MixerHttpClient$2.call(MixerHttpClient.java:205)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

[MJRLegends]

#72 would be a better fix btw, this the quick and dirty way to get things working again