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)
diff --git a/src/if_ruby.c b/src/if_ruby.c
index 9c91f31..bf7aa1a 100644
--- a/src/if_ruby.c
+++ b/src/if_ruby.c
@@ -1262,7 +1262,7 @@
     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;
 }
diff --git a/src/version.c b/src/version.c
index 729f650..114539a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    848,
+/**/
     847,
 /**/
     846,