title: Way to change Jenkins' project variable value with script
body: <p>Is there a way to change project variable values in Jenkins automatically when build is done?
  In my case i got a variable VERSION, default value is 1. And i need to increment this default value every build done. Assuming build stars by cron in this case. Any plugins can help me?</p>
  
  <p>Now i have something like this: <a href="https://i.stack.imgur.com/8H92T.png" rel="nofollow noreferrer">My build steps</a>.
  It is a single working way to get project variable in my groovy script that i found. Now how can i set new value for variable? 
  I read some similar question on SO, but didn't found a working way for me.</p>
  
  <p>P.S. I can't use $BUILD_NUMBER var, because i need a possibility to set VERSION manually when i start build.</p>