upgrade to jsbeautify v1.5.4

Importantly to some projects, JsBeautify 1.5.2 introduced ES6 module support. I have upgraded JsFormat's dependency to the latest version of JsBeautify to enable users to take advantage of this and other enhancements in the library.

As an aside, thank you for creating such an awesome plugin! It is one of my "must-haves" that I recommend to all my coworkers.