api: add build tag for go 1.7

Author: andrestc

api/client.go

@@ -11,6 +11,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.7
+
 // Package api provides clients the HTTP API's.
 package api
 

api/client_test.go

@@ -11,6 +11,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.7
+
 package api
 
 import (

api/prometheus/v1/api.go

@@ -11,6 +11,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.7
+
 // Package v1 provides bindings to the Prometheus HTTP API v1:
 // http://prometheus.io/docs/querying/api/
 package v1

api/prometheus/v1/api_test.go

@@ -11,6 +11,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.7
+
 package v1
 
 import (