fix target platform for tests ( 1.5 => 1.6 )

Author: enricosada

tests/fsharp/single-test-build.bat

@@ -127,7 +127,7 @@ set platform=win7-x64
 For %%A in ("%cd%") do (Set TestCaseName=%%~nxA)
 set command_line_args=
 set command_line_args=%command_line_args% --exec %~d0%~p0..\fsharpqa\testenv\src\deployProj\CompileProj.fsx
-set command_line_args=%command_line_args% --targetPlatformName:.NETStandard,Version=v1.5/%platform%
+set command_line_args=%command_line_args% --targetPlatformName:.NETStandard,Version=v1.6/%platform%
 set command_line_args=%command_line_args% --source:"%~d0%~p0coreclr_utilities.fs" --source:"%sources%" 
 set command_line_args=%command_line_args% --packagesDir:%~d0%~p0..\..\packages 
 set command_line_args=%command_line_args% --projectJsonLock:%~d0%~p0project.lock.json