Fix source string parse

Fix cases then variable name length in cmd is bigger than 1.

For example if i use @{foreach m in model.persons} it's ok, cuz index 12 is right beside the 'm', but if i want to use @{foreach person in model.persons} i got 'in model.persons' in cmd.substring(index).trim() and then i got syntax error in eval(fn). It worked somehow before i run npm update, but now — all my views that uses @{foreach} crashed.