patch 8.1.0421: MS-Windows: Ruby path is wrong for Ruby 1.9 and later

Problem:    MS-Windows: Ruby path is wrong for Ruby 1.9 and later.
Solution:   Let -I argument depend on Ruby version. (Ken Takata, closes #3461)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 919f0f0..1a3978c 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -1136,7 +1136,7 @@
 CFLAGS = $(CFLAGS) -DFEAT_RUBY
 RUBY_OBJ = $(OUTDIR)\if_ruby.obj
 !if $(RUBY_VER) >= 19
-RUBY_INC = /I "$(RUBY)\lib\ruby\$(RUBY_API_VER_LONG)\$(RUBY_PLATFORM)" /I "$(RUBY)\include\ruby-$(RUBY_API_VER_LONG)" /I "$(RUBY)\include\ruby-$(RUBY_API_VER_LONG)\$(RUBY_PLATFORM)"
+RUBY_INC = /I "$(RUBY)\include\ruby-$(RUBY_API_VER_LONG)" /I "$(RUBY)\include\ruby-$(RUBY_API_VER_LONG)\$(RUBY_PLATFORM)"
 !else
 RUBY_INC = /I "$(RUBY)\lib\ruby\$(RUBY_API_VER_LONG)\$(RUBY_PLATFORM)"
 !endif