Update dependencies, and drop support for node 6

(closes osmlab#230)

tap requires node 8 now

Author: bhousel

.travis.yml

@@ -1,5 +1,5 @@
 language: node_js
 node_js:
-  - "6"
   - "8"
   - "10"
+  - "12"

package.json

@@ -28,19 +28,19 @@
     "bytes": "^3.0.0",
     "colors": "^1.1.2",
     "easy-table": "^1.1.1",
-    "eslint": "^5.0.0",
+    "eslint": "^5.16.0",
     "geojson-precision": "^0.4.0",
     "geojson-rewind": "^0.3.1",
     "glob": "^7.1.0",
-    "js-yaml": "^3.11.0",
+    "js-yaml": "^3.13.1",
     "json-stringify-pretty-compact": "^1.1.0",
     "jsonschema": "^1.1.0",
     "rollup": "^1.10.0",
     "rollup-plugin-json": "^4.0.0",
     "shelljs": "^0.8.0",
-    "tap": "^14.0.0"
+    "tap": "^14.1.0"
   },
   "engines": {
-    "node": ">=4.0.0"
+    "node": ">=8.0.0"
   }
 }