[gtksourceview] build: Fix introspection on Visual Studio

[Chun-wei Fan <fanchunwei src gnome org>]

commit a00ed7fe71ed2f08d2624424d4821ecaa71774a8
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Fri Oct 5 18:07:20 2018 +0800

    build: Fix introspection on Visual Studio
    
    We ought to check for GTK+-3.x, not 4.x.

 win32/gtksourceview4-introspection-msvc.mak | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/win32/gtksourceview4-introspection-msvc.mak b/win32/gtksourceview4-introspection-msvc.mak
index 4c292668..e38353b4 100644
--- a/win32/gtksourceview4-introspection-msvc.mak
+++ b/win32/gtksourceview4-introspection-msvc.mak
@@ -4,7 +4,7 @@
 
 APIVERSION = 4
 
-CHECK_PACKAGE = gtk+-4.0
+CHECK_PACKAGE = gtk+-3.0
 
 built_install_girs = GtkSource-$(APIVERSION).gir
 built_install_typelibs = GtkSource-$(APIVERSION).typelib