patch 8.1.0848: cannot build with Ruby 1.8

Problem:    Cannot build with Ruby 1.8. (Tom G. Christensen)
Solution:   Use rb-str_new2(). (Yasuhiro Matsumoto, closes #3883,
            closes #3884)

Author: brammool

src/if_ruby.c

@@ -1262,7 +1262,7 @@ static VALUE vim_blob(VALUE self UNUSED, VALUE str)
     for (i = 0; i < RSTRING_LEN(str); i++)
     {
 	sprintf(buf, "%02X", RSTRING_PTR(str)[i]);
-	rb_str_concat(result, rb_str_new_cstr(buf));
+	rb_str_concat(result, rb_str_new2(buf));
     }
     return result;
 }

src/version.c

@@ -783,6 +783,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    848,
 /**/
     847,
 /**/