Add test for line number in HEREDOC with method call

[judofyr]

This is currently failing in JRuby (see jruby/jruby#7272).

[headius]

No need to use eval here; just stick the multi-line heredoc directly into the lambda and use some __LINE__ math for the expectation. Thanks for putting together a spec!

[judofyr]

Not sure if __LINE__ math makes it simpler though. That could make it quite fragile? E.g. suddenly it depends on the number of lines between the assertion and the code?

[eregon]

That's fine, it's already used in many places, and the CI will notice immediately if the number of lines in between changes.

[andrykonchin]

Thank you!