Adject linter to allow anonymous async functions in mocha

Specifically, this change makes this linter error go away:

    /Users/me/git/particle-api-js/test/Particle.spec.js:941:78: Parsing error: Unexpected token => [Error]`

Author: Joe Goggins

.eslintrc.js

@@ -1,7 +1,8 @@
 module.exports = {
 	extends: ['eslint-config-particle'],
 	parserOptions: {
-		sourceType: 'module'
+		sourceType: 'module',
+		ecmaVersion: 8
 	},
 	env: {
 		browser: true,