require external dependencies in main file

src/mechanize.cr

@@ -1,3 +1,5 @@
+require "uri"
+require "http/client"
 require "lexbor"
 require "./mechanize/http/agent"
 require "./mechanize/form"

src/mechanize/file.cr

@@ -1,5 +1,3 @@
-require "http/client"
-
 class Mechanize
   abstract class File
     # property :filename

src/mechanize/http/agent.cr

@@ -1,5 +1,3 @@
-require "uri"
-require "http/client"
 require "../cookie"
 require "../history"