Update search to use v2 API endpoint

v1 has been disabled on most instances by now.
The change is minor: hash-tags are now reported as proper structs
instead of a simple string-array.

mastodon.go

@@ -319,7 +319,7 @@ type Emoji struct {
 type Results struct {
 	Accounts []*Account `json:"accounts"`
 	Statuses []*Status  `json:"statuses"`
-	Hashtags []string   `json:"hashtags"`
+	Hashtags []*Tag     `json:"hashtags"`
 }
 
 // Pagination is a struct for specifying the get range.