fixed compile error

example/example.vcxproj

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -51,19 +51,19 @@
     <ProjectGuid>{9E5AB93A-0CCE-4BAC-9FCB-0FC9CB5EB8D2}</ProjectGuid>
     <Keyword>Win32Proj</Keyword>
     <RootNamespace>.</RootNamespace>
-    <WindowsTargetPlatformVersion>8.1</WindowsTargetPlatformVersion>
+    <WindowsTargetPlatformVersion>10.0.16299.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <UseDebugLibraries>true</UseDebugLibraries>
-    <PlatformToolset>v120</PlatformToolset>
+    <PlatformToolset>v141</PlatformToolset>
     <CharacterSet>Unicode</CharacterSet>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
-    <PlatformToolset>v120</PlatformToolset>
+    <PlatformToolset>v141</PlatformToolset>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
   </PropertyGroup>

include/spdlog/details/traits.h

@@ -28,7 +28,7 @@ namespace spdlog {
 			using mutex_t = std::mutex;			
 			static mutex_t& console_mutex()
 			{ 
-				static auto mutex = mutex_t{};
+				static auto &mutex = mutex_t{};
 				return mutex;
 			}
 		};