[evolution] README.md: Update WebKitGTK+ version, to match the one in CMakeLists.txt

[Milan Crha <mcrha src gnome org>]

commit 4da845f1366c12e31c3aa95e80942cffb6203315
Author: Milan Crha <mcrha redhat com>
Date:   Mon Apr 27 16:10:40 2020 +0200

    README.md: Update WebKitGTK+ version, to match the one in CMakeLists.txt

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index 375a6ba271..45abb13bc6 100644
--- a/README.md
+++ b/README.md
@@ -50,7 +50,7 @@ dependencies should be compiled in the order they are listed here):
 
 * [evolution-data-server of the same version as the Evolution is][eds]
 * [libsoup 2.42 or later][libsoup]
-* [WebKitGTK+ 2.16.0][webkitgtk]
+* [WebKitGTK+ 2.28.0][webkitgtk]
 * [Mozilla NSPR/NSS libraries][mozilla]
   These are needed if you want to compile Evolution with SSL and S/MIME
   support. Many distributions ship these as Mozilla development packages.