Remove /v6 from import path

This commit removes the `/v6` from the import path and reverts the Go
module from `github.com/olivere/elastic/v6` to just
`github.com/olivere/elastic`.

The reason for that is that existing tools like `dep` and `glide`
currently don't support minimal module-awareness and are therefor
confused with the trailing `/v6`. Go 1.9.7, Go 1.10.4 and Go 1.11 have
this kind of module-awareness now, but tooling lacks a bit behind.

This makes it impossible for Elastic to be a good citizen for both
camps, and we need to delay 100% Go modules support to a later release.

.travis.yml

@@ -9,7 +9,7 @@ matrix:
   - go: tip
 env:
 - GO111MODULE=on
-- GO111MODULE=auto
+- GO111MODULE=off
 addons:
   ssh_known_hosts: github.com
   apt:

example_test.go

@@ -14,7 +14,6 @@ import (
 	"time"
 
 	"github.com/olivere/elastic"
-	// "github.com/olivere/elastic/v6" // <- with Go modules
 )
 
 type Tweet struct {

go.mod

@@ -1,9 +1,8 @@
-module github.com/olivere/elastic/v6
+module github.com/olivere/elastic
 
 require (
 	github.com/fortytw2/leaktest v1.2.0
 	github.com/mailru/easyjson v0.0.0-20180823135443-60711f1a8329
-	github.com/olivere/elastic v6.1.25+incompatible
 	github.com/opentracing/opentracing-go v1.0.2
 	github.com/pkg/errors v0.8.0
 	github.com/smartystreets/go-aws-auth v0.0.0-20180515143844-0c1422d1fdb9

recipes/go-modules/main.go

@@ -8,7 +8,7 @@
 // Example
 //
 //
-//     go run main.go -url=http://127.0.0.1:9200 -sniff=false
+//     GO111MODULE=on go run main.go -url=http://127.0.0.1:9200 -sniff=false
 //
 package main
 
@@ -17,7 +17,7 @@ import (
 	"fmt"
 	"log"
 
-	"github.com/olivere/elastic/v6"
+	"github.com/olivere/elastic" // <- should end with /v6, but missing due to compatibility reasons
 )
 
 func main() {