Tiny fix : SolutionDir not ProjectDir

The lines in

https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworksCompiled/proje
ct/vs/openFrameworksDebug.props#L24
https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworksCompiled/project/vs/openFrameworksDebug.props#L41
https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworksCompiled/project/vs/openFrameworksRelease.props#L23
https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworksCompiled/project/vs/openFrameworksRelease.props#L39

should be

<Command>robocopy "$(OF_ROOT)/export/vs/$(Platform_Actual)/" "$(SolutionDir)bin/" "*.dll" /njs /njh /np /fp /bytes
if errorlevel 1 exit 0 else exit %errorlevel%</Command>

not

<Command>robocopy "$(OF_ROOT)/export/vs/$(Platform_Actual)/" "$(ProjectDir)bin/" "*.dll" /njs /njh /np /fp /bytes
if errorlevel 1 exit 0 else exit %errorlevel%</Command>

or just $(TargetDir)

Mostly this doesn't matter
but it can matter if you're building DLL's from openFrameworks code (which are generally output to the solution dir, not the project dir)

Start with the four referenced files: libs/openFrameworksCompiled/project/vs/openFrameworksDebug.props and openFrameworksRelease.props, at the linked command lines. Compare the robocopy destination variables with the issue description, update the affected commands consistently, and verify that DLLs built from openFrameworks code are copied to the solution's bin directory.