improve error message when ) is missing on prev line

[cppforlife]

when closing ) is missing on a prev line error message got identifier, want ',' pops up. since ytt shows error related line it's a bit confusing that ) is missing on the prev line.

• https://get-ytt.io/#gist:https://gist.github.com/cppforlife/c34961a5e9a5aa31a16d6d678ed28f96
• https://get-ytt.io/#gist:https://gist.github.com/cppforlife/8c7088cab2b7b64752fbc4481cac5a17

should we add some hint to indicate this similar to this: https://github.com/k14s/ytt/blob/582ad9ca849559e5d75b680b1831105059a0e953/pkg/template/error_hints_test.go

[benjaminapetersen]

Bump on this. I do ytt on occasion, but not enough to remain fluent at all times. This one has gotten me a few times. Would love even a hint syntax error or perhaps you forgot to close a function? or something.