test: fix node 4 test

tap 12.0.1 was a security release, but depended on nyc@13 which doesn't
support node 4 (tapjs/tapjs#479). Fortunately, v12.1.1 has been
released to fix that. Bumping the version here to bust caches that may
still think 12.1.0 is the best match.

Signed-off-by: Ryan Graham <r.m.graham@gmail.com>

package.json

@@ -30,7 +30,7 @@
     "minimist": "^1.2.0"
   },
   "devDependencies": {
-    "tap": "^12.0.1"
+    "tap": "^12.1.1"
   },
   "engines": {
     "node": ">=4"