Definition of arrow function:
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions

Example ES6 Javascript:

var materialsLength3 = materials.map(material=> material.length);

Error raised :
1 | ERROR | [x] Expected 1 space before "="; 0 found
1 | ERROR | [x] Expected 1 space after "="; 0 found
1 | ERROR | [x] Equals sign not aligned correctly; expected 1 space but found 0 spaces
1 | ERROR | [x] Expected 1 space before ">"; 0 found

Expectation:
No error.

Other: File is OperatorSpacingSniff.php. In 3.0 ./src/Standards/Squiz/Sniffs/WhiteSpace/OperatorSpacingSniff.php