api/go1.13: add debug/elf.Symbol fields added in CL 184099

These will need auditing per #32813 like a few others in go1.13.txt, but
in the meantime they break the API check for beta/RC releases.

Updates #32813
Updates #31912

Change-Id: I3b0501b46324ee6fc0985f84971b99b772c7e4a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/189458Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

api/go1.13.txt

@@ -39,6 +39,8 @@ pkg debug/dwarf, method (*UnsupportedType) String() string
 pkg debug/dwarf, type UnsupportedType struct
 pkg debug/dwarf, type UnsupportedType struct, embedded CommonType
 pkg debug/dwarf, type UnsupportedType struct, Tag Tag
+pkg debug/elf, type Symbol struct, Library string
+pkg debug/elf, type Symbol struct, Version string
 pkg encoding/csv, method (*ParseError) Unwrap() error
 pkg encoding/json, method (*MarshalerError) Unwrap() error
 pkg errors, func As(error, interface{}) bool