revert tap update to test on node 6

Note: this will be re-applied in the next semver major bump.

Author: isaacs

.travis.yml

@@ -1,7 +1,7 @@
 language: node_js
 sudo: false
 node_js:
+  - "12"
   - "10"
   - "8"
   - "6"
-  - "11"

package-lock.json

@@ -8,7 +8,7 @@
     "postrelease": "npm publish && git push --follow-tags",
     "pretest": "standard",
     "release": "standard-version -s",
-    "test": "tap",
+    "test": "tap -J --cov test/*.js",
     "update-coc": "weallbehave -o . && git add CODE_OF_CONDUCT.md && git commit -m 'docs(coc): updated CODE_OF_CONDUCT.md'",
     "update-contrib": "weallcontribute -o . && git add CONTRIBUTING.md && git commit -m 'docs(contributing): updated CONTRIBUTING.md'"
   },
@@ -43,7 +43,7 @@
     "sinon": "^7.2.3",
     "standard": "^12.0.1",
     "standard-version": "^4.4.0",
-    "tap": "^13.1.3",
+    "tap": "^12.7.0",
     "weallbehave": "^1.2.0",
     "weallcontribute": "^1.0.8"
   },