Visual Studio 2017 build fix

Author: florianbecker

source/FileLogger.cpp

@@ -82,7 +82,7 @@ namespace vx {
     output.append( timestamp() );
 
     std::string severity = std::string( magic_enum::enum_name( _severity ) );
-    std::transform( severity.begin(), severity.end(), severity.begin(), []( unsigned char c ) { return std::toupper( c ); } );
+    std::transform( severity.begin(), severity.end(), severity.begin(), []( unsigned char c ) { return ::toupper( c ); } );
     output.append( " [" + severity + "] " );
     output.append( _message );
     output.push_back( '\n' );

source/StdLogger.cpp

@@ -58,7 +58,7 @@ namespace vx {
     output.append( timestamp() );
 
     std::string severity = std::string( magic_enum::enum_name( _severity ) );
-    std::transform( severity.begin(), severity.end(), severity.begin(), []( unsigned char c ) { return std::toupper( c ); } );
+    std::transform( severity.begin(), severity.end(), severity.begin(), []( unsigned char c ) { return ::toupper( c ); } );
     if ( m_useColor ) {
 
       switch ( _severity ) {

source/XmlFileLogger.cpp

@@ -57,7 +57,7 @@ namespace vx {
     output.append( "</timestamp>" );
 
     std::string severity = std::string( magic_enum::enum_name( _severity ) );
-    std::transform( severity.begin(), severity.end(), severity.begin(), []( unsigned char c ) { return std::toupper( c ); } );
+    std::transform( severity.begin(), severity.end(), severity.begin(), []( unsigned char c ) { return ::toupper( c ); } );
     output.append( "<severity>" );
     output.append( severity );
     output.append( "</severity>" );