lint: add Unwrap to common methods

Change-Id: Ia2f9aa6efeaff0d22a04af54340ccefdf0598f9a
GitHub-Last-Rev: 354a28341b0ec697300e0ce9160c7709b29b1981
GitHub-Pull-Request: golang/lint#487
Reviewed-on: https://go-review.googlesource.com/c/lint/+/221610
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

lint.go

diff --git a/lint.go b/lint.go
index 532a75a..7d813e0 100644
--- a/lint.go
+++ b/lint.go
@@ -839,6 +839,7 @@
 	"ServeHTTP": true,
 	"String":    true,
 	"Write":     true,
+	"Unwrap":    true,
 }
 
 // lintFuncDoc examines doc comments on functions and methods.

testdata/common-methods.go

diff --git a/testdata/common-methods.go b/testdata/common-methods.go
index c0bb136..e2377bd 100644
--- a/testdata/common-methods.go
+++ b/testdata/common-methods.go
@@ -14,3 +14,4 @@
 func (T) ServeHTTP(w http.ResponseWriter, r *http.Request) {}
 func (T) Read(p []byte) (n int, err error)                 { return 0, nil }
 func (T) Write(p []byte) (n int, err error)                { return 0, nil }
+func (T) Unwrap(err error) error                           { return nil }