incorrect typeof checks in a few places causing unintended behaviour

[jokeyrhyme]

Describe the bug

moment's code include incorrect uses of typeof that are causing the Symbol support check to fail in Node.js 0.10.x, and maybe causing issues with the use of __dirname

moment.js
2093:                    (typeof __dirname !== undefined ? __dirname : '.') +
4917:    if (typeof Symbol !== undefined && Symbol.for != null) {

min/moment-with-locales.js
2087:                    (typeof __dirname !== undefined ? __dirname : '.') +
4911:    if (typeof Symbol !== undefined && Symbol.for != null) {

src/lib/moment/prototype.js
61:if (typeof Symbol !== undefined && Symbol.for != null) {

src/lib/locale/locales.js
79:                (typeof __dirname !== undefined ? __dirname : '.') +

Note that typeof returns a string, and the above checks are comparing the result of typeof against the undefined value, not the "undefined" string

To Reproduce
Steps to reproduce the behavior:

1. require('moment') using a version of Node.js that doesn't implement Symbol
2. observe the following error:

if (typeof Symbol !== undefined && Symbol.for != null) {
ReferenceError: Symbol is not defined

Expected behavior
This should load just fine without any exceptions or errors

Screenshots
n/a

[jokeyrhyme]

ESLint has a rule to check for invalid uses of typeof that you may find useful: https://eslint.org/docs/rules/valid-typeof

[ichernev]

@jokeyrhyme we have eslint and we use "extends": "eslint:recommended" and it still didn't catch it. Maybe you can investigate.

I'll fix the typeof problems and release shortly.