patch 8.1.0797: error E898 is used twice

Problem:    Error E898 is used twice.
Solution:   Rename the Blob error to E899. (closes #3853)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 325676d..3db9151 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -38,7 +38,7 @@
 1. Variables						*variables*
 
 1.1 Variable types ~
-						*E712* *E896* *E897* *E898*
+						*E712* *E896* *E897* *E899*
 There are nine types of variables:
 
 Number		A 32 or 64 bit signed number.  |expr-number| *Number*