pipe out stderr and stdout from popen2e command

Gemfile.lock

 GIT
   remote: git@gitlab.coko.foundation:INK/ink-step.git
-  revision: f6b2175c1b870cbc9f43e8b57b01545072ba41ea
+  revision: 3b5cdc06d93ef5814cf29e39a1fd491f58c69ddb
   specs:
-    ink_step (0.1.9)
+    ink_step (0.1.10)
       awesome_print
       httparty
       rubyzip
@@ -10,7 +10,7 @@ GIT
 PATH
   remote: .
   specs:
-    inkstep_coko_conversion (0.2.6)
+    inkstep_coko_conversion (0.2.8)
 
 GEM
   remote: https://rubygems.org/

lib/coko_conversion/ink_step/vivliostyle_to_pdf_step.rb

@@ -38,7 +38,7 @@ module InkStep
 
       command = "Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &"
 
-      perform_command(command: command, error_prefix: "error running Xvfb")
+      perform_command(command: command, print_out: true, error_prefix: "error running Xvfb")
     end
 
     def run_vivliostyle_conversion(source_file_path, destination_file_path)

lib/coko_conversion/version.rb

 module CokoConversion
-  VERSION = '0.2.7'
+  VERSION = '0.2.8'
 end
\ No newline at end of file