from @alexholman, copied from codecombat/codecombat#3710

Related to my initial issue report: codecombat/codecombat#3709
I found my problem was typing =+ instead of += for an increment, resulting in an infinite loop condition.

This is not a very informative error for this easy typo. The code should catch the use of =+ and warn, much like it catches capitalization issues in object names and missing ':' in loops.