fix isFile bug

was previously using `fs.lstatSync().isFile()`. The `isFile()` method doesnt seem to exist so i went with `fs.existsSync()` instead.

lib/node.js

@@ -3,16 +3,16 @@ import fs from "fs"
 
 
 export const Node = {
-    isFile:function(filename){
+  isFile: function(filename) {
     try {
-            return fs.lstatSync(filename).isFile()
+      return fs.existsSync(filename)
     } catch (err) {
-            console.log(err)
+      console.error(err)
       return false
     }
 
   },
-    getFullPath:function(folderPath){
+  getFullPath: function(folderPath) {
     return fs.readdirSync(folderPath).map(fn => path.join(folderPath, fn))
   },
   getFiles: function(dir) {
@@ -31,11 +31,11 @@ export const Node = {
     });
     return results.filter(f => f.endsWith(".md"))
   },
-    readFileSync:function(fullPath){
+  readFileSync: function(fullPath) {
     return fs.readFileSync(fullPath, "utf8")
   },
 
-    getMarkdownFolder: function () {
+  getMarkdownFolder: function() {
     return path.join(process.cwd(), 'posts')
   }
 }