patch 8.0.0961: the script to build the installer does not include winpty

Problem:    The script to build the installer does not include winpty.
Solution:   Add winpty32.dll and winpty-agent.exe like diff.exe
diff --git a/nsis/gvim.nsi b/nsis/gvim.nsi
index dba9021..b424392 100644
--- a/nsis/gvim.nsi
+++ b/nsis/gvim.nsi
@@ -191,13 +191,16 @@
 	File ${VIMSRC}\vimrun.exe
 	File /oname=tee.exe ${VIMSRC}\teew32.exe
 	File /oname=xxd.exe ${VIMSRC}\xxdw32.exe
-	File ${VIMTOOLS}\diff.exe
 	File ${VIMRT}\vimtutor.bat
 	File ${VIMRT}\README.txt
 	File ..\uninstal.txt
 	File ${VIMRT}\*.vim
 	File ${VIMRT}\rgb.txt
 
+	File ${VIMTOOLS}\diff.exe
+	File ${VIMTOOLS}\winpty32.dll
+	File ${VIMTOOLS}\winpty-agent.exe
+
 	SetOutPath $0\colors
 	File ${VIMRT}\colors\*.*