Fix global leaks detected by mocha

Fix globals leaked in stringUtils, isJson and static/nav.html.

lib/stringUtils.js

@@ -3,8 +3,7 @@ function hashCode(string){
 	var hash = 0;
 	if (string.length == 0) return hash;
 	for (let i = 0; i < string.length; i++) {
-		char = string.charCodeAt(i);
-		hash = ((hash << 5) - hash) + char;
+		hash = ((hash << 5) - hash) + string.charCodeAt(i);
 		hash = hash & hash; // Convert to 32bit integer
 	}
 	return hash;

sharedPlugins/inventoryImports/isJson.js

@@ -2,7 +2,7 @@ module.exports = function(x){
 	if(x === false || x === true || x === null) return true; // === false is valid JSON, so is true and null
 	var isNotJson = false
 	try{
-		z = JSON.parse(x);
+		JSON.parse(x);
 	} catch (e) {
 		isNotJson = true;
 	}

static/nav.html

@@ -13,7 +13,7 @@
     </div>
     <%# Very ugly ejs code to hide the Players button if the playerManager plugin isn`t installed %>
     <%
-    sidebarPluginButtonsHtml = "";
+    let sidebarPluginButtonsHtml = "";
     for(let o in locals.masterPlugins){
     let plug = locals.masterPlugins[o];
     if(plug.main