MM-12389 Update segment library to v3 (#11472)

* Update analytics-go dependency

* Migrate from segment library v2 to v3

* Reinclude gorilla/handlers module

* Fix missing module

* Remove reference to outdated analytics module

vendor/github.com/segmentio/analytics-go/Readme.md

@@ -1,8 +1,55 @@
-# analytics-go
+# analytics-go [![Circle CI](https://circleci.com/gh/segmentio/analytics-go/tree/master.svg?style=shield)](https://circleci.com/gh/segmentio/analytics-go/tree/master) [![go-doc](https://godoc.org/github.com/segmentio/analytics-go?status.svg)](https://godoc.org/github.com/segmentio/analytics-go)
 
-  Segment analytics client for Go. For additional documentation
-  visit [https://segment.com/docs/libraries/go](https://segment.com/docs/libraries/go/) or view the [godocs](http://godoc.org/github.com/segmentio/analytics-go).
+Segment analytics client for Go.
+
+## Installation
+
+The package can be simply installed via go get, we recommend that you use a
+package version management system like the Go vendor directory or a tool like
+Godep to avoid issues related to API breaking changes introduced between major
+versions of the library.
+
+To install it in the GOPATH:
+```
+go get https://github.com/segmentio/analytics-go
+```
+
+## Documentation
+
+The links bellow should provide all the documentation needed to make the best
+use of the library and the Segment API:
+
+- [Documentation](https://segment.com/docs/libraries/go/)
+- [godoc](https://godoc.org/gopkg.in/segmentio/analytics-go.v3)
+- [API](https://segment.com/docs/libraries/http/)
+- [Specs](https://segment.com/docs/spec/)
+
+## Usage
+
+```go
+package main
+
+import (
+    "os"
+
+    "github.com/segmentio/analytics-go"
+)
+
+func main() {
+    // Instantiates a client to use send messages to the segment API.
+    client := analytics.New(os.Getenv("SEGMENT_WRITE_KEY"))
+
+    // Enqueues a track event that will be sent asynchronously.
+    client.Enqueue(analytics.Track{
+        UserId: "test-user",
+        Event:  "test-snippet",
+    })
+
+    // Flushes any queued messages and closes the client.
+    client.Close()
+}
+```
 
 ## License
 
- MIT
+The library is released under the [MIT license](License.md).