fixed JSONification contract

`#toJSON` is not supposed to stringify the respective value itself:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#toJSON()_behavior

/cc @moonglum

Author: FND

lib/manifest.js

@@ -43,15 +43,14 @@ module.exports = class Manifest {
 		this._index.set(key, uri);
 
 		let fp = this.filepath;
-		return fp ? createFile(fp, this.toJSON()) : Promise.resolve(null);
+		return fp ? createFile(fp, JSON.stringify(this) + "\n") : Promise.resolve(null);
 	}
 
 	toJSON() {
 		let index = this._index;
-		let manifest = Array.from(index.keys()).sort().reduce((memo, key) => {
+		return Array.from(index.keys()).sort().reduce((memo, key) => {
 			memo[key] = index.get(key);
 			return memo;
 		}, {});
-		return JSON.stringify(manifest) + "\n";
 	}
 };

package.json

@@ -25,15 +25,15 @@
 		"lint": "eslint --cache lib bin/* test test/bin/* && echo ✓"
 	},
 	"dependencies": {
-		"browserslist": "~4.3.0",
+		"browserslist": "~4.3.4",
 		"minimist": "~1.2.0",
 		"mkdirp": "~0.5.1",
 		"nite-owl": "~3.3.2"
 	},
 	"devDependencies": {
 		"eslint-config-fnd": "^1.6.0",
 		"mocha": "^5.2.0",
-		"npm-run-all": "^4.1.3",
+		"npm-run-all": "^4.1.5",
 		"release-util-fnd": "^1.1.1"
 	}
 }

test/test_manifest.js

@@ -24,19 +24,19 @@ describe("manifest", _ => {
 		let manifest = new Manifest(root);
 		return manifest.set("foo.png", "foo-abc123.png").
 			then(_ => { // eslint-disable-next-line quotes
-				assertSame(manifest.toJSON(), `{"foo.png":"/foo-abc123.png"}\n`);
+				assertSame(JSON.stringify(manifest), `{"foo.png":"/foo-abc123.png"}`);
 
 				return manifest.set("bar.css", "bar-def456.css");
 			}).
 			then(_ => {
-				assertSame(manifest.toJSON(), // eslint-disable-next-line quotes
-						`{"bar.css":"/bar-def456.css","foo.png":"/foo-abc123.png"}\n`);
+				assertSame(JSON.stringify(manifest), // eslint-disable-next-line quotes
+						`{"bar.css":"/bar-def456.css","foo.png":"/foo-abc123.png"}`);
 
 				return manifest.set("xox.js", "xox-ghi789.js");
 			}).
 			then(_ => {
-				assertSame(manifest.toJSON(), // eslint-disable-next-line quotes
-						`{"bar.css":"/bar-def456.css","foo.png":"/foo-abc123.png","xox.js":"/xox-ghi789.js"}\n`);
+				assertSame(JSON.stringify(manifest), // eslint-disable-next-line quotes
+						`{"bar.css":"/bar-def456.css","foo.png":"/foo-abc123.png","xox.js":"/xox-ghi789.js"}`);
 			});
 	});
 });