Examples: DirectX11: fixed vertex shader which breaks with VS2015 somehow (DX11 version?) (#313)

examples/directx11_example/imgui_impl_dx11.cpp

@@ -293,7 +293,7 @@ bool    ImGui_ImplDX11_CreateDeviceObjects()
     // Create the vertex shader
     {
         static const char* vertexShader = 
-            "cbuffer vertexBuffer : register(c0) \
+            "cbuffer vertexBuffer : register(b0) \
             {\
             float4x4 ProjectionMatrix; \
             };\