move http-form_data to test dependencies block

Gemfile

@@ -9,6 +9,7 @@ gem "rake", "~> 12.3"
 
 group :test do
   gem "ddtrace"
+  gem "http-form_data", ">= 2.0.0"
   gem "minitest"
   gem "minitest-proveit"
   gem "webmock"

httpx.gemspec

@@ -32,5 +32,4 @@ Gem::Specification.new do |gem|
 
   gem.add_runtime_dependency "http-2-next", ">= 0.1.2"
   gem.add_runtime_dependency "timers"
-  gem.add_development_dependency "http-form_data", ">= 2.0.0", "< 3"
 end

lib/httpx/plugins/multipart.rb

@@ -50,10 +50,6 @@ module HTTPX
         end
       end
 
-      def self.load_dependencies(*)
-        require "http/form_data"
-      end
-
       def self.configure(*)
         Transcoder.register("form", FormTranscoder)
       end