doc: fix outdated output msg in the assert example [av skip]

(cherry picked from commit e10e039)
ref #13928

Author: gloine

doc/manual/metaprogramming.rst

@@ -545,7 +545,7 @@ This macro can be used like this:
     julia> @assert 1==1.0
 
     julia> @assert 1==0
-    ERROR: AssertionError: 1 == 0
+    ERROR: Assertion failed: 1 == 0
 
 In place of the written syntax, the macro call is expanded at parse time to
 its returned result. This is equivalent to writing::