fix: added defensive check against process.stdin (#5)

Instead of assuming that `process.stdin` will return an object, add a check to make sure that it does before trying to access `process.stdin.isTTY`.

Author: rramphal

lib/index.js

@@ -220,7 +220,7 @@ if (typeof module !== 'undefined') {
   module.exports.afterLine = afterLine;
   if (!module.parent) {
     // cli mode
-    if (!process.stdin.isTTY) {
+    if (process.stdin && !process.stdin.isTTY) {
       const stdinBuffer = require('fs').readFileSync(0); // STDIN_FILENO = 0
       console.log(module.exports(JSON.parse(stdinBuffer.toString())));
     }