fix unlinkSync call in runtests.js

AUTHORS.rst

@@ -49,6 +49,7 @@ and agreed to irrevocably license their contributions under the Duktape
 * Jakub Nowakowski (https://github.com/jimvonmoon)
 * Tommy Nguyen (https://github.com/tn0502)
 * Fabrice Fontaine (https://github.com/ffontaine)
+* Christopher Hiller (https://github.com/boneskull)
 
 Other contributions
 ===================

runtests/runtests.js

@@ -44,7 +44,7 @@ function mkTempName(ext) {
 function safeUnlinkSync(filePath) {
     try {
         if (filePath) {
-            fs.unlink(filePath);
+            fs.unlinkSync(filePath);
         }
     } catch (e) {
         console.log('Failed to unlink ' + filePath + ' (ignoring): ' + e);