chore: update eslint-plugin-unicorn to ^16.0.0

BREAKING CHANGE: eslint-plugin-unicorn requires Node.js 10
(sindresorhus/eslint-plugin-unicorn@d2ffe2c) and changes the
number-literal-case to require lower-case 'e'
(sindresorhus/eslint-plugin-unicorn#490).

Fixes: #8

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

package.json

@@ -36,7 +36,7 @@
     "eslint-config-airbnb-base": "^14.0.0",
     "eslint-plugin-node": "^11.0.0",
     "eslint-plugin-promise": "^4.2.1",
-    "eslint-plugin-unicorn": "^15.0.0"
+    "eslint-plugin-unicorn": "^16.0.0"
   },
   "devDependencies": {
     "eclint": "^2.8.1",
@@ -46,12 +46,12 @@
     "eslint-plugin-import": "^2.18.2",
     "eslint-plugin-node": "^11.0.0",
     "eslint-plugin-promise": "^4.2.1",
-    "eslint-plugin-unicorn": "^15.0.0",
+    "eslint-plugin-unicorn": "^16.0.0",
     "greenkeeper-lockfile": "^1.15.1",
     "peer-version-check": "^0.1.0"
   },
   "engines": {
-    "node": ">=8.3",
+    "node": ">=10",
     "npm": ">=1.3.7"
   }
 }