Upgrade to Babel 7 (#523)

* Run npx babel-upgrade, removing unnecessary stage0 plugins

* Move from babel-preset-node6 to @babel/preset-env

* Update nyc to work with updated babel

.babelrc

@@ -1,3 +1,15 @@
 {
-  "presets": ["node6", "stage-0"]
+  "presets": [
+    [
+      "@babel/preset-env",
+      {
+        "targets": {
+          "node": "6"
+        }
+      }
+    ]
+  ],
+  "plugins": [
+    "istanbul"
+  ]
 }

.nycrc

@@ -0,0 +1,3 @@
+{
+  "extends": "@istanbuljs/nyc-config-babel"
+}

package.json

@@ -27,7 +27,7 @@
     "build": "babel lib --out-dir dist",
     "prepare": "npm run build",
     "lint": "eslint . --ignore-path .gitignore",
-    "coverage": "nyc --require babel-core/register _mocha -- 'test/*.test.js'",
+    "coverage": "nyc --require @babel/register mocha -- 'test/*.test.js'",
     "report": "nyc report --reporter=text-lcov | coveralls",
     "test": "npm run lint && npm run coverage"
   },
@@ -48,11 +48,13 @@
     "winston": "3.2.1"
   },
   "devDependencies": {
-    "babel-cli": "^6.6.5",
-    "babel-core": "^6.26.3",
+    "@babel/cli": "^7.0.0",
+    "@babel/core": "^7.0.0",
+    "@babel/preset-env": "^7.7.6",
+    "@babel/register": "^7.7.4",
+    "@istanbuljs/nyc-config-babel": "^2.1.1",
     "babel-eslint": "^10.0.1",
-    "babel-preset-node6": "^11.0.0",
-    "babel-preset-stage-0": "^6.5.0",
+    "babel-plugin-istanbul": "^5.2.0",
     "chai": "^4.2.0",
     "coveralls": "^3.0.4",
     "eslint": "^5.16.0",