BUG: fixed compilation error in Visual Studio 2017 15.8

Status Job ID Name Coverage
  External
passed cdash

passed ghostflow-branch-check-master

passed imstk-liones-linux-shared-debug

passed imstk-liones-linux-shared-release

passed imstk-marvin-windows-shared-debug+msvc2013+omni

passed imstk-marvin-windows-shared-release+msvc2013+omni

passed imstk-norkit-osx-shared-debug

passed imstk-norkit-osx-shared-release

passed imstk-liones-linux-shared-debug

00:04:55

passed imstk-liones-linux-shared-release

00:03:14

passed imstk-marvin-windows-shared-debug+msvc2013+omni

00:03:03

passed imstk-marvin-windows-shared-release+msvc2013+omni

00:00:26

passed imstk-norkit-osx-shared-debug

00:04:56

passed imstk-norkit-osx-shared-release

00:03:16