Fix heredocs with leading spaces

[jemmaissroff]

puts <<-'    ABC'
marker with spaces
    ABC

puts <<~'    ABC'
marker with spaces
    ABC

Worth noting that this behavior recently changed upstream:

• bug report
• fix

[kddnewton]

@haldun do you think you could take a look at this one?

[kddnewton]

@haldun if it's alright, I'm going to assign this one to you. I know we talked about pairing on it, which we can do next week.

[kddnewton]

Ahh nvm... I guess I can't assign it to you?

[kddnewton]

@haldun I just invited to the repository, let me know when you accept and then I'll assign this one to you.

[haldun]

Accepted.