Problem: Tests do no build in Windows environment

Solution: Modified CMakelist.txt to build correctly for Windows
- corrected CMake required version to make sure it builds in
  Ubuntu 14.04 LTS with no warnings.

tests/CMakeLists.txt

 # CMake build script for ZeroMQ tests
-cmake_minimum_required(VERSION "3.0")
+cmake_minimum_required(VERSION "2.8.1")
 
 # name of Windows project will tests.sln
 PROJECT(tests)