Removed npm prepare instruction

Author: mickys

package.json

@@ -14,7 +14,6 @@
     "build": "rimraf dist/* && tsc --emitDeclarationOnly && cross-env NODE_ENV=production webpack --config webpack.config.js",
     "test": "jest -c jest.config.js",
     "publish": "yarn build && yarn publish",
-    "prepare": "npm run build"
   },
   "dependencies": {
     "bn.js": "^4.11.8",