redmine-backporter.rb: Remove an unneeded space

from #backport_command_string

I don't want to leave unneeded spaces in the command history by
copy-pasting the entire line.

tool/redmine-backporter.rb

@@ -194,7 +194,7 @@ def backport_command_string
     end
     @changesets.define_singleton_method(:validated){true}
   end
-  " #{merger_path} --ticket=#{@issue} #{@changesets.sort.join(',')}"
+  "#{merger_path} --ticket=#{@issue} #{@changesets.sort.join(',')}"
 end
 
 def status_char(obj)