Add env option

Author: BuonOmo

README.md

@@ -183,6 +183,7 @@ Ferrum::Browser.new(options)
       than this will cause a `Ferrum::DeadBrowserError`.
   * `:proxy` (Hash) - Specify proxy settings, [read more](https://github.com/rubycdp/ferrum#proxy)
   * `:save_path` (String) - Path to save attachments with [Content-Disposition](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Disposition) header.
+  * `:env` (Hash) - Environment variables you'd like to pass through to the process
 
 
 ## Navigation

lib/ferrum/browser/process.rb

@@ -73,6 +73,7 @@ def initialize(options)
 
         @logger = options[:logger]
         @process_timeout = options.fetch(:process_timeout, PROCESS_TIMEOUT)
+        @env = Hash(options[:env])
 
         tmpdir = Dir.mktmpdir("ferrum_user_data_dir_")
         ObjectSpace.define_finalizer(self, self.class.directory_remover(tmpdir))
@@ -95,7 +96,8 @@ def start
             ObjectSpace.define_finalizer(self, self.class.process_killer(@xvfb.pid))
           end
 
-          @pid = ::Process.spawn(Hash(@xvfb&.to_env), *@command.to_a, process_options)
+          env = Hash(@xvfb&.to_env).merge(@env)
+          @pid = ::Process.spawn(env, *@command.to_a, process_options)
           ObjectSpace.define_finalizer(self, self.class.process_killer(@pid))
 
           parse_ws_url(read_io, @process_timeout)