Fix linting errors

.eslintrc.json

@@ -1,8 +1,8 @@
 {
 	"env": {
-		"browser": true,
 		"commonjs": true,
-		"es6": true
+		"es6": true,
+		"node": true
 	},
 	"extends": "eslint:recommended",
 	"globals": {

src/parser.js

@@ -176,7 +176,7 @@ function populateFrontmatter(posts) {
 	posts.forEach(post => {
 		const frontmatter = {};
 		settings.frontmatter_fields.forEach(field => {
-			[key, alias] = field.split(':');
+			const [key, alias] = field.split(':');
 
 			let frontmatterGetter = frontmatterGetters[key];
 			if (!frontmatterGetter) {