fix: error on missing entry

closes #467

closes #464

test/fixture/dependency.js

@@ -0,0 +1 @@
+module.exports = 'abc'

test/fixture/entry.js

@@ -0,0 +1 @@
+console.log('hello world', require('./dependency'))

test/fixture/package.json

@@ -1,3 +1,3 @@
 {
-  "main": "entry-file.js"
+  "main": "entry.js"
 }