fix: set the client user agent

The code already existed for setting the UserAgent header, but a value
was never passed to the client. This change will now set a string
matching the following format

```
faas-cli/<build version>
```

For example:

```
faas-cli/0.14.6-5-ga9c2b10f
```

Signed-off-by: Lucas Roesler <roesler.lucas@gmail.com>

proxy/client.go

@@ -11,6 +11,8 @@ import (
 	gopath "path"
 	"strings"
 	"time"
+
+	"github.com/openfaas/faas-cli/version"
 )
 
 // Client an API client to perform all operations
@@ -51,6 +53,7 @@ func NewClient(auth ClientAuth, gatewayURL string, transport http.RoundTripper,
 		ClientAuth: auth,
 		httpClient: client,
 		GatewayURL: baseURL,
+		UserAgent:  fmt.Sprintf("faas-cli/%s", version.BuildVersion()),
 	}, nil
 }
 

version/version.go

@@ -1,7 +1,5 @@
 package version
 
-const UserAgent = "OpenFaaS CLI"
-
 var (
 	Version, GitCommit string
 )