Package.json can't be found bugfix (#170)

* add path traversing for package.json, plugin bug

* improve

* fix

* add another test

src/Bundler.js

@@ -88,13 +88,20 @@ class Bundler extends EventEmitter {
     this.packagers.add(type, packager);
   }
 
-  loadPlugins() {
+  loadPlugins(location = this.mainFile) {
+    let pkg;
+    try {
+      pkg = localRequire('./package.json', location);
+    } catch (err) {
+      if (err.code === 'MODULE_NOT_FOUND' && location.length > 1) {
+        return this.loadPlugins(Path.join(location, '..'));
+      }
+    }
     try {
-      let pkg = localRequire('./package.json', this.mainFile);
       let deps = Object.assign({}, pkg.dependencies, pkg.devDependencies);
       for (let dep in deps) {
         if (dep.startsWith('parcel-plugin-')) {
-          localRequire(dep, this.mainFile)(this);
+          localRequire(dep, location)(this);
         }
       }
     } catch (err) {

test/integration/plugins/sub-folder/index.js

@@ -0,0 +1 @@
+module.exports = require('./test.txt');

test/integration/plugins/sub-folder/test.txt

@@ -0,0 +1 @@
+hello world

test/plugins.js

@@ -14,4 +14,17 @@ describe('plugins', function() {
     let output = run(b);
     assert.equal(output, 'hello world');
   });
+
+  it('should load package.json from parent tree', async function() {
+    let b = await bundle(__dirname + '/integration/plugins/sub-folder/index.js');
+
+    assertBundleTree(b, {
+      name: 'index.js',
+      assets: ['index.js', 'test.txt'],
+      childBundles: []
+    });
+
+    let output = run(b);
+    assert.equal(output, 'hello world');
+  });
 });