Changed the args to subprocess.Popen to pass args to the command

Before the command was not working correctly to check the calibre version since it seemed to be treating the entire string as the command.  So when ' --version' was added it was breaking.  I changed the format to pass the command and args as a list and it seems to work correctly.

cps/converter.py

@@ -34,7 +34,7 @@ def versionCalibre():
     versions = _(u'not installed')
     if os.path.exists(ub.config.config_converterpath):
         try:
-            p = subprocess.Popen(ub.config.config_converterpath + ' --version', stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+            p = subprocess.Popen([ub.config.config_converterpath, '--version'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
             p.wait()
             for lines in p.stdout.readlines():
                 if isinstance(lines, bytes):