Remove dependency on golang.org/x/xerrors (#407)

The errors.Is func and support for error wrapping using the %w verb are
available since Go 1.13, see https://blog.golang.org/go1.13-errors

The go.mod file already specifies Go 1.14 as the minimum supported
version, so it's safe to drop the transitional golang.org/x/xerrors
dependency.

go.mod

@@ -6,6 +6,5 @@ require (
 	github.com/golang/protobuf v1.4.2
 	github.com/onsi/ginkgo v1.12.1
 	golang.org/x/net v0.0.0-20201202161906-c7110b5ffcbb
-	golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
 	gopkg.in/yaml.v2 v2.3.0
 )

go.sum

@@ -27,10 +27,6 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd h1:nTDtHvHSdCn1m6ITfMRqtOd/9+7a3s8RBNOZ3eYZzJA=
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/net v0.0.0-20200520004742-59133d7f0dd7 h1:AeiKBIuRw3UomYXSbLy0Mc2dDLfdtbT/IVn4keq83P0=
-golang.org/x/net v0.0.0-20200520004742-59133d7f0dd7/go.mod h1:qpuaurCH72eLCgpAm/N6yyVIVM9cpaDIP3A8BGJEC5A=
-golang.org/x/net v0.0.0-20201006153459-a7d1128ccaa0 h1:wBouT66WTYFXdxfVdz9sVWARVd/2vfGcmI45D2gj45M=
-golang.org/x/net v0.0.0-20201006153459-a7d1128ccaa0/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20201202161906-c7110b5ffcbb h1:eBmm0M9fYhWpKZLjQUUKka/LtIxf46G4fxeEz5KJr9U=
 golang.org/x/net v0.0.0-20201202161906-c7110b5ffcbb/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f h1:wMNYb4v58l5UBM7MYRLPG6ZhfOqbKu7X5eyFl8ZhKvA=
@@ -42,8 +38,6 @@ golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20190904154756-749cb33beabd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191120155948-bd437916bb0e h1:N7DeIrjYszNmSW409R3frPPwglRwMkXSBzwVbkOjLLA=
 golang.org/x/sys v0.0.0-20191120155948-bd437916bb0e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd h1:xhmwyvizuTgC2qz7ZlMluP20uW+C3Rm0FD/WLDX8884=
-golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f h1:+Nyd8tzPX9R7BWHguqsrbFdRx3WQ/1ib8I44HXV5yTA=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=

matchers/match_error_matcher.go

@@ -1,11 +1,11 @@
 package matchers
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 
 	"github.com/onsi/gomega/format"
-	"golang.org/x/xerrors"
 )
 
 type MatchErrorMatcher struct {
@@ -25,7 +25,7 @@ func (matcher *MatchErrorMatcher) Match(actual interface{}) (success bool, err e
 	expected := matcher.Expected
 
 	if isError(expected) {
-		return reflect.DeepEqual(actualErr, expected) || xerrors.Is(actualErr, expected.(error)), nil
+		return reflect.DeepEqual(actualErr, expected) || errors.Is(actualErr, expected.(error)), nil
 	}
 
 	if isString(expected) {

matchers/match_error_matcher_test.go

@@ -7,7 +7,6 @@ import (
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 	. "github.com/onsi/gomega/matchers"
-	"golang.org/x/xerrors"
 )
 
 type CustomError struct {
@@ -34,7 +33,7 @@ var _ = Describe("MatchErrorMatcher", func() {
 
 			It("should succeed when any error in the chain matches the passed error", func() {
 				innerErr := errors.New("inner error")
-				outerErr := xerrors.Errorf("outer error wrapping: %w", innerErr)
+				outerErr := fmt.Errorf("outer error wrapping: %w", innerErr)
 
 				Expect(outerErr).Should(MatchError(innerErr))
 			})