Use the same cmake_minimum_required version 3.1 (#847)

c72578 · BillyONeal · commit b14f9ff6c48a · 2018-10-01T15:13:21.000-07:00
as in Release/CMakeLists.txt
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.1)
 project(cpprestsdk-root NONE)
 
 add_subdirectory(Release)
