Rename Result.Headers to Result.Header.

This way, it's consistent with http.Header in the response.
diff --git a/openstack/objectstorage/v1/objects/requests.go b/openstack/objectstorage/v1/objects/requests.go
index 49dc9f5..13d94f8 100644
--- a/openstack/objectstorage/v1/objects/requests.go
+++ b/openstack/objectstorage/v1/objects/requests.go
@@ -133,7 +133,7 @@
 	body, err := ioutil.ReadAll(resp.HttpResponse.Body)
 	res.Body = body
 	res.Err = err
-	res.Headers = resp.HttpResponse.Header
+	res.Header = resp.HttpResponse.Header
 	return res
 }
 
@@ -218,7 +218,7 @@
 		MoreHeaders: h,
 		OkCodes:     []int{201},
 	})
-	res.Headers = resp.HttpResponse.Header
+	res.Header = resp.HttpResponse.Header
 	res.Err = err
 	return res
 }
@@ -274,7 +274,7 @@
 		MoreHeaders: h,
 		OkCodes:     []int{201},
 	})
-	res.Headers = resp.HttpResponse.Header
+	res.Header = resp.HttpResponse.Header
 	return res
 }
 
@@ -316,7 +316,7 @@
 		MoreHeaders: c.Provider.AuthenticatedHeaders(),
 		OkCodes:     []int{204},
 	})
-	res.Headers = resp.HttpResponse.Header
+	res.Header = resp.HttpResponse.Header
 	res.Err = err
 	return res
 }
@@ -361,7 +361,7 @@
 		MoreHeaders: c.Provider.AuthenticatedHeaders(),
 		OkCodes:     []int{200, 204},
 	})
-	res.Headers = resp.HttpResponse.Header
+	res.Header = resp.HttpResponse.Header
 	res.Err = err
 	return res
 }
@@ -418,7 +418,7 @@
 		MoreHeaders: h,
 		OkCodes:     []int{202},
 	})
-	res.Headers = resp.HttpResponse.Header
+	res.Header = resp.HttpResponse.Header
 	res.Err = err
 	return res
 }
diff --git a/openstack/objectstorage/v1/objects/results.go b/openstack/objectstorage/v1/objects/results.go
index 45a1048..e662b69 100644
--- a/openstack/objectstorage/v1/objects/results.go
+++ b/openstack/objectstorage/v1/objects/results.go
@@ -64,7 +64,7 @@
 // ExtractNames is a function that takes a page of objects and returns only their names.
 func ExtractNames(page pagination.Page) ([]string, error) {
 	casted := page.(ObjectPage)
-	ct := casted.Headers.Get("Content-Type")
+	ct := casted.Header.Get("Content-Type")
 	switch {
 	case strings.HasPrefix(ct, "application/json"):
 		parsed, err := ExtractInfo(page)
@@ -122,7 +122,7 @@
 		return nil, gr.Err
 	}
 	metadata := make(map[string]string)
-	for k, v := range gr.Headers {
+	for k, v := range gr.Header {
 		if strings.HasPrefix(k, "X-Object-Meta-") {
 			key := strings.TrimPrefix(k, "X-Object-Meta-")
 			metadata[key] = v[0]
@@ -138,7 +138,7 @@
 // Extract returns the unmodified HTTP response headers from a Create, Update, or Delete call, as
 // well as any errors that occurred during the call.
 func (result headerResult) Extract() (http.Header, error) {
-	return result.Headers, result.Err
+	return result.Header, result.Err
 }
 
 // CreateResult represents the result of a create operation.