updated additional contributors list

Author: aherrera1721

CONTRIBUTORS.md

@@ -33,6 +33,7 @@ We are certain the list is incomplete; please let one of us know by opening an [
 + [@0dminnimda](https://github.com/0dminnimda)
 + Mike Miller ([@Axe319](https://github.com/axe319))
 + Dan Miller ([@danx0r(https://github.com/danx0r))
++ Alex Herrera ([@aherrera1721](https://github.com/aherrera1721))
 
 ## Full timeline of vpython development