IllegalThreadStateException in HttpClientHelper.requestAsync (HttpClientHelper.java:100)

[joshgontijo]

From #92

We're getting this error when calling requestAsync parallel during performance testing our application with gatling.

java.lang.IllegalThreadStateException: null
at java.lang.Thread.start(Thread.java:705) ~[na:1.8.0_40]
at com.mashape.unirest.http.HttpClientHelper.requestAsync(HttpClientHelper.java:100) ~[unirest-java-1.4.5.jar:na]
at com.mashape.unirest.request.BaseRequest.asStringAsync(BaseRequest.java:64) ~[unirest-java-1.4.5.jar:na]