adds extra check for browser common.js
adds extra check for browser common.js

I've been trying to use tcp-socket from within an electron app and I
stumbled upon a problem: navigator is present, so it detects it as a
common.js for browser when node.js `net` and `tls` could be used.

martindale/tcp-socket,huangxok/tcp-socket,martindale/tcp-socket,emailjs/emailjs-tcp-socket,emailjs/emailjs-tcp-socket,huangxok/tcp-socket,whiteout-io/tcp-socket,klorenz/tcp-socket,klorenz/tcp-socket,whiteout-io/tcp-socket,emailjs/emailjs-tcp-socket