Update ws dependency to 7.1.2

Also fix the license identifier that `npm audit` complains about.

Testing Done:

* `npm test`
* Ran [example/index.html]() and saw chart live update

package.json

@@ -41,7 +41,7 @@
  "sse.js": "^0.4.1",
  "text-encoding": "^0.6.4",
  "winston": "^1.0.1",
- "ws": "^1.1.0"
+ "ws": "^7.1.2"
  },
  "scripts": {
  "prepublish": "gulp prepublish",
@@ -51,5 +51,5 @@
  "engines": {
  "npm": ">=4.0.0"
  },
- "license": "Apache Software License v2"
+ "license": "Apache-2.0"
 }