Update README with proper case

[willieconrad]

In the README, there's an example of using ngECharts in a browser, with a script tag pointing to bower_components/ngecharts/dist/ngecharts.min.js, even though when you bower install the package it installs to bower_components/ngECharts/dist/ngecharts.min.js. For the most part, this case mismatch doesn't matter. However, if you are using gulp or some such tool to optimize all the JS in your project, it will scan your script tags for file to optimize, and if you are on a case-sensitive filesystem, it will fail to find this file. So probably best to update the README to use the same case as what's on disk.