normalize mocha spec duration in snapshot

__snapshots__/mocha-snapshot-spec.js

@@ -18,7 +18,7 @@ exports['captures mocha output 1'] = `
       ✓ works
 
 
-    1 passing (10ms)
+    1 passing (<time>ms)
   -------
   stderr:
   -------

scripts/mocha-snapshot-spec.js

@@ -6,6 +6,7 @@ function normalize (s) {
   // and the command is hardcoded in package.json
   // using forward slashes
   return s.replace(process.cwd(), '<folder path>')
+    .replace(/passing \(\d+ms\)/, 'passing (<time>ms)')
 }
 
 /* eslint-env mocha */