Added file detection for *.SVG files when working with folders (#1316)

Currently, files named *.SVG are not being detected under Windows because of the case-sensitivity. This commit includes these in addition to *.svg files.

lib/svgo/coa.js

@@ -8,7 +8,7 @@ const { loadConfig, optimize } = require('../svgo-node.js');
 const pluginsMap = require('../../plugins/plugins.js');
 const PKG = require('../../package.json');
 const { encodeSVGDatauri, decodeSVGDatauri } = require('./tools.js');
-const regSVGFile = /\.svg$/;
+const regSVGFile = /\.svg$/i;
 const noop = () => {};
 
 /**