feat(upstream) add Algorithm field to Upstream struct

Kong 1.3 adds an `algorithm` field to the Upstream entity.

From #9

kong/upstream.go

@@ -56,6 +56,7 @@ type Healthcheck struct {
 type Upstream struct {
 	ID                 *string      `json:"id,omitempty" yaml:"id,omitempty"`
 	Name               *string      `json:"name,omitempty" yaml:"name,omitempty"`
+	Algorithm          *string      `json:"algorithm,omitempty" yaml:"algorithm,omitempty"`
 	Slots              *int         `json:"slots,omitempty" yaml:"slots,omitempty"`
 	Healthchecks       *Healthcheck `json:"healthchecks,omitempty" yaml:"healthchecks,omitempty"`
 	CreatedAt          *int64       `json:"created_at,omitempty" yaml:"created_at,omitempty"`

kong/upstream_service_test.go

@@ -124,6 +124,28 @@ func TestUpstreamWithPassiveUnHealthyInterval(T *testing.T) {
 	assert.Nil(createdUpstream)
 }
 
+func TestUpstreamWithAlgorithm(T *testing.T) {
+	runWhenKong(T, ">=1.3.0")
+	assert := assert.New(T)
+
+	client, err := NewClient(nil, nil)
+	assert.Nil(err)
+	assert.NotNil(client)
+
+	upstream := &Upstream{
+		Name:      String("upstream1"),
+		Algorithm: String("least-connections"),
+	}
+
+	createdUpstream, err := client.Upstreams.Create(defaultCtx, upstream)
+	assert.Nil(err)
+	assert.NotNil(createdUpstream)
+	assert.Equal("least-connections", *createdUpstream.Algorithm)
+
+	err = client.Upstreams.Delete(defaultCtx, createdUpstream.ID)
+	assert.Nil(err)
+}
+
 func TestUpstreamListEndpoint(T *testing.T) {
 	assert := assert.New(T)