Update mattermost library (#2152)

* Update mattermost library

* Fix linting

vendor/github.com/hashicorp/go-hclog/README.md

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+# go-hclog
+
+[![Go Documentation](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)][godocs]
+
+[godocs]: https://godoc.org/github.com/hashicorp/go-hclog
+
+`go-hclog` is a package for Go that provides a simple key/value logging
+interface for use in development and production environments.
+
+It provides logging levels that provide decreased output based upon the
+desired amount of output, unlike the standard library `log` package.
+
+It provides `Printf` style logging of values via `hclog.Fmt()`.
+
+It provides a human readable output mode for use in development as well as
+JSON output mode for production.
+
+## Stability Note
+
+This library has reached 1.0 stability. Its API can be considered solidified
+and promised through future versions.
+
+## Installation and Docs
+
+Install using `go get github.com/hashicorp/go-hclog`.
+
+Full documentation is available at
+http://godoc.org/github.com/hashicorp/go-hclog
+
+## Usage
+
+### Use the global logger
+
+```go
+hclog.Default().Info("hello world")
+```
+
+```text
+2017-07-05T16:15:55.167-0700 [INFO ] hello world
+```
+
+(Note timestamps are removed in future examples for brevity.)
+
+### Create a new logger
+
+```go
+appLogger := hclog.New(&hclog.LoggerOptions{
+	Name:  "my-app",
+	Level: hclog.LevelFromString("DEBUG"),
+})
+```
+
+### Emit an Info level message with 2 key/value pairs
+
+```go
+input := "5.5"
+_, err := strconv.ParseInt(input, 10, 32)
+if err != nil {
+	appLogger.Info("Invalid input for ParseInt", "input", input, "error", err)
+}
+```
+
+```text
+... [INFO ] my-app: Invalid input for ParseInt: input=5.5 error="strconv.ParseInt: parsing "5.5": invalid syntax"
+```
+
+### Create a new Logger for a major subsystem
+
+```go
+subsystemLogger := appLogger.Named("transport")
+subsystemLogger.Info("we are transporting something")
+```
+
+```text
+... [INFO ] my-app.transport: we are transporting something
+```
+
+Notice that logs emitted by `subsystemLogger` contain `my-app.transport`,
+reflecting both the application and subsystem names.
+
+### Create a new Logger with fixed key/value pairs
+
+Using `With()` will include a specific key-value pair in all messages emitted
+by that logger.
+
+```go
+requestID := "5fb446b6-6eba-821d-df1b-cd7501b6a363"
+requestLogger := subsystemLogger.With("request", requestID)
+requestLogger.Info("we are transporting a request")
+```
+
+```text
+... [INFO ] my-app.transport: we are transporting a request: request=5fb446b6-6eba-821d-df1b-cd7501b6a363
+```
+
+This allows sub Loggers to be context specific without having to thread that
+into all the callers.
+
+### Using `hclog.Fmt()`
+
+```go
+totalBandwidth := 200
+appLogger.Info("total bandwidth exceeded", "bandwidth", hclog.Fmt("%d GB/s", totalBandwidth))
+```
+
+```text
+... [INFO ] my-app: total bandwidth exceeded: bandwidth="200 GB/s"
+```
+
+### Use this with code that uses the standard library logger
+
+If you want to use the standard library's `log.Logger` interface you can wrap
+`hclog.Logger` by calling the `StandardLogger()` method. This allows you to use
+it with the familiar `Println()`, `Printf()`, etc. For example:
+
+```go
+stdLogger := appLogger.StandardLogger(&hclog.StandardLoggerOptions{
+	InferLevels: true,
+})
+// Printf() is provided by stdlib log.Logger interface, not hclog.Logger
+stdLogger.Printf("[DEBUG] %+v", stdLogger)
+```
+
+```text
+... [DEBUG] my-app: &{mu:{state:0 sema:0} prefix: flag:0 out:0xc42000a0a0 buf:[]}
+```
+
+Alternatively, you may configure the system-wide logger:
+
+```go
+// log the standard logger from 'import "log"'
+log.SetOutput(appLogger.StandardWriter(&hclog.StandardLoggerOptions{InferLevels: true}))
+log.SetPrefix("")
+log.SetFlags(0)
+
+log.Printf("[DEBUG] %d", 42)
+```
+
+```text
+... [DEBUG] my-app: 42
+```
+
+Notice that if `appLogger` is initialized with the `INFO` log level, _and_ you
+specify `InferLevels: true`, you will not see any output here. You must change
+`appLogger` to `DEBUG` to see output. See the docs for more information.
+
+If the log lines start with a timestamp you can use the
+`InferLevelsWithTimestamp` option to try and ignore them. Please note that in order
+for `InferLevelsWithTimestamp` to be relevant, `InferLevels` must be set to `true`.