copy-webpack-plugin should be a dev dependency

[minht11]

It is only used during development thus not needed for users to install as a dependency.

iterable-web-sdk/webpack.dev.config.js

Lines 1 to 5 in 3948ff5

	const path = require('path');
	const env = require('dotenv').config({ path: './.env' });
	const webpack = require('webpack');
	const { version } = require('./package.json');
	const CopyPlugin = require('copy-webpack-plugin');