Change codeplex wiki reference to github

Author: alexkaratarakis

Release/src/pplx/threadpool.cpp

@@ -33,7 +33,7 @@ static void abort_if_no_jvm()
 {
     if (JVM == nullptr)
     {
-        __android_log_print(ANDROID_LOG_ERROR, "CPPRESTSDK", "%s", "The CppREST SDK must be initialized before first use on android: https://casablanca.codeplex.com/wikipage?title=Use%20on%20Android");
+        __android_log_print(ANDROID_LOG_ERROR, "CPPRESTSDK", "%s", "The CppREST SDK must be initialized before first use on android: https://github.com/Microsoft/cpprestsdk/wiki/How-to-build-for-Android");
         std::abort();
     }
 }