lint: don't use lambdas for non-lambda stuff

[coolaj86]

It's confusing to use mathematical lambdas where you're not returning a value or doing math

[markin-io]

Arrow functions in JS could be used in any circumstances, there are no obligatory rules to return value or do the math.
I don't think that having this change is critical. @thephez it's up to you

[coolaj86]

Arrow functions in JS could be used in any circumstances

Usefulness is not a great argument for code style.

* 1 is useful for turning a string into a number (or + '' a number into a string)

! is useful as a replacement for ; between function executions

1.. is useful as a substitute for (1)

There are many anti-semantic things you can do in JavaScript, but they're confusing and signal the wrong thing to the reader of the code.

lambdas signal that you intend to return the evaluation of a mathematical expression in-line. That's what they're for.