Resolves: rhbz#1702810 Prepare for upcoming libebook soname version bump

as noted here:
https://mail.gnome.org/archives/desktop-devel-list/2019-April/msg00016.html

wrt:
https://gitlab.gnome.org/GNOME/evolution-data-server/issues/33

Change-Id: I88f900b3adf12de545b1d2d16da67eae22fde748
Reviewed-on: https://gerrit.libreoffice.org/71282Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
Tested-by: Jenkins

connectivity/source/drivers/evoab2/EApi.cxx

@@ -21,6 +21,7 @@
 #define  DECLARE_FN_POINTERS 1
 #include "EApi.h"
 static const char *eBookLibNames[] = {
+    "libebook-1.2.so.20", // evolution-data-server 3.33.2+
     "libebook-1.2.so.19", // evolution-data-server 3.24+
     "libebook-1.2.so.16",
     "libebook-1.2.so.15",