Revert to using strings for simplicity

It is safe in this case.

* gock.BodyString(body string) coerces body into a []byte
* client.SetData() eventually resolves to a call to http.Client.Do(), which
handles the string gracefully as well.

internal/client/set_test.go

@@ -1,8 +1,8 @@
 package client_test
 
 import (
-	"bytes"
 	"net/http"
+	"strings"
 	"testing"
 
 	gock "gopkg.in/h2non/gock.v1"
@@ -21,7 +21,7 @@ func TestSetDataSuccessOnCorrectRequest(t *testing.T) {
 		"http://localhost:8080",
 		"HANDLER_FOO",
 		"/response/status/code",
-		bytes.NewReader([]byte("200")),
+		strings.NewReader("200"),
 	); err != nil {
 		t.Error("Unexpected error")
 	}
@@ -42,7 +42,7 @@ func TestSetDataErrIfBadHandlerID(t *testing.T) {
 		"http://localhost:8080",
 		"HANDLER_BAD",
 		"/response/status/code",
-		bytes.NewReader([]byte("200")),
+		strings.NewReader("200"),
 	); err == nil {
 		t.Error("Expected error not present")
 	} else if err.Error() != "Not Found" {