Upgrade yargs to ^17.2.1

.travis.yml

@@ -1,11 +1,10 @@
 language: node_js
 branches: [master]
 node_js:
+  - 16
+  - 15
   - 14
   - 13
   - 12
-  - 10
-  - 8
-  - 6
 before_script: ./bin/sassgraph descendents test/fixtures test/fixtures/simple/index.scss
 after_success: npm run coverage

package.json

@@ -21,7 +21,7 @@
     "glob": "^7.0.0",
     "lodash": "^4.17.11",
     "scss-tokenizer": "^0.3.0",
-    "yargs": "^13.3.2"
+    "yargs": "^17.2.1"
   },
   "devDependencies": {
     "assert": "^1.3.0",
@@ -31,7 +31,7 @@
     "nyc": "^13.1.0"
   },
   "engines": {
-    "node": ">= 4"
+    "node": ">=12"
   },
   "files": [
     "bin",