Add changeset task

Author: gksander

package.json

@@ -16,7 +16,8 @@
  "test-ts-defs": "tsc --target ES5 index.d.ts",
  "test": "builder concurrent --buffer eslint tslint test-ts-usage test-ts-defs test-node-cov test-browser",
  "compress": "terser --compress --mangle=\"toplevel:true\" -- index.js",
- "size-min-gz": "yarn -s compress | gzip -9 | wc -c"
+ "size-min-gz": "yarn -s compress | gzip -9 | wc -c",
+ "changeset": "changeset"
  },
  "repository": {
  "type": "git",
@@ -102,4 +103,4 @@
  "index.d.ts"
  ],
  "types": "index.d.ts"
-}
+}