patch 8.1.0871: build error when building with Ruby 2.6.0

Problem:    Build error when building with Ruby 2.6.0.
Solution:   Change argument of rb_int2big_stub(). (Android Baumann,
            closes #3899)

src/version.c

@@ -783,6 +783,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    871,
 /**/
     870,
 /**/