Fix kwargs warnings on Ruby 2.7

See https://www.ruby-lang.org/en/news/2019/12/12/separation-of-positional-and-keyword-arguments-in-ruby-3-0/

Author: janko

spec/lib/http/form_data/multipart_spec.rb

@@ -57,7 +57,7 @@ def disposition(params)
 
     context "with filename set to nil" do
       let(:part) { HTTP::FormData::Part.new("s", :content_type => "mime/type") }
-      let(:form_data) { HTTP::FormData::Multipart.new(:foo => part) }
+      let(:form_data) { HTTP::FormData::Multipart.new({ :foo => part }) }
 
       it "doesn't include a filename" do
         boundary_value = form_data.content_type[/(#{boundary})$/, 1]
@@ -74,7 +74,7 @@ def disposition(params)
 
     context "with content type set to nil" do
       let(:part) { HTTP::FormData::Part.new("s") }
-      let(:form_data) { HTTP::FormData::Multipart.new(:foo => part) }
+      let(:form_data) { HTTP::FormData::Multipart.new({ :foo => part }) }
 
       it "doesn't include a filename" do
         boundary_value = form_data.content_type[/(#{boundary})$/, 1]

spec/lib/http/form_data/part_spec.rb

@@ -3,7 +3,7 @@
 RSpec.describe HTTP::FormData::Part do
   let(:body)     { "" }
   let(:opts)     { {} }
-  subject(:part) { HTTP::FormData::Part.new(body, opts) }
+  subject(:part) { HTTP::FormData::Part.new(body, **opts) }
 
   describe "#size" do
     subject { part.size }