Upgrade to Go 1.7 (#128)

* Upgrade to stdlib context package
* Modernized syntax

api/server/server.go

@@ -1,13 +1,12 @@
 package server
 
 import (
+	"context"
 	"encoding/json"
 	"io/ioutil"
 	"net/http"
 	"path"
 
-	"golang.org/x/net/context"
-
 	"github.com/Sirupsen/logrus"
 	"github.com/gin-gonic/gin"
 	"github.com/iron-io/functions/api/ifaces"