Fix module path to have the major version to comply with go modules

specs as specified in https://github.com/golang/go/wiki/Modules#semantic-import-versioning

.travis.yml

@@ -1,5 +1,5 @@
 language: go
-go_import_path: go.etcd.io/etcd
+go_import_path: go.etcd.io/etcd/v3
 
 sudo: required
 

client/keys.go

@@ -25,7 +25,6 @@ import (
 	"strconv"
 	"strings"
 	"time"
-
 )
 
 const (

proxy/grpcproxy/cache/store.go

@@ -21,7 +21,6 @@ import (
 	"sync"
 
 	"github.com/golang/groupcache/lru"
-
 	"go.etcd.io/etcd/v3/etcdserver/api/v3rpc/rpctypes"
 	pb "go.etcd.io/etcd/v3/etcdserver/etcdserverpb"
 	"go.etcd.io/etcd/v3/pkg/adt"

test

@@ -617,6 +617,9 @@ function commit_title_pass {
 	done
 }
 
+# tools gosimple,unused,staticheck,unconvert,ineffasign,nakedret
+# are not module-aware. See https://github.com/golang/go/issues/24661
+# The module-aware versions need to be used when they become available
 function fmt_pass {
 	toggle_failpoints disable
 
@@ -628,13 +631,7 @@ function fmt_pass {
 			gofmt \
 			govet \
 			govet_shadow \
-			gosimple \
-			unused \
-			staticcheck \
 			revive \
-			unconvert \
-			ineffassign \
-			nakedret \
 			license_header \
 			receiver_name \
 			commit_title \
@@ -649,6 +646,12 @@ function bom_pass {
 	if ! command -v license-bill-of-materials >/dev/null; then
 		return
 	fi
+	if [ "${GO111MODULE}" == "on" ]; then
+		# license-bill-off-materials calls "go list std cmd" which cannot handle modules
+		# Please see https://github.com/golang/go/issues/26924
+		echo "Skipping license-bill-of-materials with go modules..."
+		return
+	fi
 	echo "Checking bill of materials..."
 	license-bill-of-materials \
 		--override-file bill-of-materials.override.json \