Fix: use global-import shelljs (#38)

* Fix: use global-import shelljs

* Add comment

lib/release-ops.js

@@ -5,15 +5,19 @@
  * MIT License
  */
 
+/* global test, cat, rm, mv */
+
 "use strict";
 
 //------------------------------------------------------------------------------
 // Requirements
 //------------------------------------------------------------------------------
 
+// TODO: Update to use non-global module to avoid prototype pollution.
+require("shelljs/global");
+
 const fs = require("fs"),
     path = require("path"),
-    shelljs = require("shelljs"),
     semver = require("semver"),
     GitHub = require("github-api"),
     dateformat = require("dateformat"),
@@ -44,7 +48,7 @@ function getPackageInfo() {
  * @private
  */
 function validateSetup() {
-    if (!shelljs.test("-f", "package.json")) {
+    if (!test("-f", "package.json")) {
         console.error("Missing package.json file");
         ShellOps.exit(1);
     }
@@ -319,15 +323,16 @@ function writeChangelog(releaseInfo) {
     (`\n${releaseInfo.rawChangelog}\n`).toEnd("CHANGELOG.tmp");
 
     // ensure there's a CHANGELOG.md file
-    if (!shelljs.test("-f", "CHANGELOG.md")) {
+    if (!test("-f", "CHANGELOG.md")) {
         fs.writeFileSync("CHANGELOG.md", "");
     }
 
     // switch-o change-o
-    fs.writeFileSync("CHANGELOG.md.tmp", shelljs.cat("CHANGELOG.tmp", "CHANGELOG.md"));
-    shelljs.rm("CHANGELOG.tmp");
-    shelljs.rm("CHANGELOG.md");
-    shelljs.mv("CHANGELOG.md.tmp", "CHANGELOG.md");
+    // `cat` returns a ShellString and `fs.writeFileSync` is throwing an error saying that this must be a String.
+    fs.writeFileSync("CHANGELOG.md.tmp", cat("CHANGELOG.tmp", "CHANGELOG.md").toString());
+    rm("CHANGELOG.tmp");
+    rm("CHANGELOG.md");
+    mv("CHANGELOG.md.tmp", "CHANGELOG.md");
 }
 
 /**