Update ws dependency to 7.1.2

Issue #50

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"
 }