Fix errors when running markdown-doctest

 - import in bin/cmd.js
 - drop lodash dependency
 - target es5 (markdown-doctest is used by a wide variety of packages,
 who run tests on all sorts of versions of nodes)

bin/cmd.js

@@ -1,7 +1,7 @@
 #! /usr/bin/env node
 'use strict';
 
-var doctest = require('../lib/doctest');
+var doctest = require('..');
 
 var fs = require('fs');
 

src/doctest.ts

@@ -5,7 +5,10 @@ import { runInNewContext } from "vm";
 import { transformSync } from "@babel/core";
 import presetEnv from "@babel/preset-env";
 import chalk from "chalk";
-import flatten from "lodash/flatten";
+
+function flatten<T>(arr: T[][]): T[] {
+  return Array.prototype.concat.apply([], arr);
+}
 
 import parseCodeSnippets, {
   Snippet,
@@ -95,7 +98,7 @@ function testFile(config: Config) {
       results = codeSnippets.map(test(config, fileName));
     }
 
-    return flatten(results);
+    return results;
   };
 }
 

tsconfig.json

@@ -1,7 +1,6 @@
 {
   "compilerOptions": {
-    "target": "es6",
-    "moduleResolution": "node",
+    "target": "es5",
     "rootDir": "src",
     "outDir": "./dist",
     "allowSyntheticDefaultImports": true