fix(gitbook-treeview): calculate headers' level

Author: aleen42

lib/index.js

@@ -148,7 +148,7 @@ const pageTreeview = module.exports = {
 
 		let minLevel = 6;
 
-		const _calcLevel = str => str.split('').filter(ch => ch === '#').length;
+		const _calcLevel = str => (/^#+/.exec(str) || [''])[0].length;
 		const headers = [].concat(content.match(/^(#)+(\s)*(.*)\n/g))
 			.concat(content.match(/\n(#)+(\s)*(.*)/g))
 			.map(x => {