The debug/dwarf and encoding/asn1 examples were added in 2009, a few
months before Go added implicit semicolons, and never updated.

The go/ast node types have always been named just "Expr", "Stmt", and
"Decl", so the comments about "ExprNode", "StmtNode", and "DeclNode"
were likely just mistaken because the interface tag methods are
"exprNode", "stmtNode", and "declNode", respectively.

Change-Id: I9d138cc3a16c1a51453da1406914d7b320bf6270
Reviewed-on: https://go-review.googlesource.com/7980Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>