Fix test script for node 4.x

Node.js 4.x does not understand default parameter values.

PR-URL: #169
Reviewed-By: Michael Dawson <[email protected]>

Author: Gabriel Schulhof

test/common/index.js

@@ -34,13 +34,16 @@ exports.mustCall = function(fn, exact) {
   return _mustCallInner(fn, exact, 'exact');
 };
 
-function _mustCallInner(fn, criteria = 1, field) {
+function _mustCallInner(fn, criteria, field) {
   if (typeof fn === 'number') {
     criteria = fn;
     fn = noop;
   } else if (fn === undefined) {
     fn = noop;
   }
+  if (criteria === undefined) {
+    criteria = 1;
+  }
 
   if (typeof criteria !== 'number')
     throw new TypeError(`Invalid ${field} value: ${criteria}`);