ci(.travis.yml): drop support for node@6

Removes support for node@6 due to approaching end of maintenance period.  This action is forced by a
dependency issue.

Author: Tbhesswebber

.travis.yml

@@ -4,7 +4,6 @@ cache:
   directories:
     - node_modules
 node_js:
-  - 6
   - 8
   - 10
   - node

package.json

@@ -8,7 +8,7 @@
   ],
   "scripts": {
     "fire": "git checkout -b emergency && git commit -Am 'emergency commit' && git push --set-upstream origin emergency --no-verify",
-    "gcommit": "git-cz",
+    "cz": "git-cz",
     "prebuild": "rimraf dist",
     "build": "npm-run-all --parallel build:*",
     "build:node": "babel src --out-dir dist --ignore 'src/*.test.js'",
@@ -159,7 +159,7 @@
   },
   "config": {
     "commitizen": {
-      "path": "./node_modules/cz-conventional-changelog"
+      "path": "cz-conventional-changelog"
     }
   }
 }