Update http dependency to > 4.3

[jrmhaig]

We are using this gem and have identified an intermittent fault after upgrading to Ruby 2.7. The http gem is pinned to version 3 but Ruby 2.7 support was added with version 4.3.0.

I have a test to demonstrate:

require 'googlemaps/services/client'

include GoogleMaps::Services

key = '<add your API key here>'
origin = 'SW1A 1AA'
destination = 'SW1A 2AA'

c = GoogleClient.new(key: key, response_format: :json)
params = { 'origin' => origin, 'destination' => destination, 'region' => 'uk', 'alternatives' => true }

10.times do |i|
  response = c.request(url: '/maps/api/directions/json', params: params)
end

At some point you get a can't modify frozen String: "" (FrozenError) error at http-3.3.0/lib/http/response/body.rb:52. This is resolved with version 4.3 or later of http.

[coveralls]

Coverage remained the same at 97.917% when pulling 46856ac on jrmhaig:update_http into 77e8d19 on amrfaissal:master.