Upgrade less to version 2 (#503)

This fixes a problem where the graceful-js dependency of the old less
version is incompatible with node 7, and will cause warnings on node 6.
The resulting katex.min.css is exactly the same as with the previous
version, so the major version upgrade does not seem to affect the outcome.

The less.Parser has been deprecated, and less.render is the supported
approach now, so we have to switch the development server to that.

package.json

@@ -24,7 +24,7 @@
     "jasmine-core": "^2.3.4",
     "js-yaml": "^3.3.1",
     "jspngopt": "^0.1.0",
-    "less": "~1.7.5",
+    "less": "~2.7.1",
     "nomnom": "^1.8.1",
     "pako": "0.2.7",
     "selenium-webdriver": "^2.46.1",

server.js

@@ -61,19 +61,18 @@ app.get("/katex.css", function(req, res, next) {
             return;
         }
 
-        var parser = new less.Parser({
+        less.render(data, {
             paths: ["./static"],
             filename: "katex.less",
-        });
-
-        parser.parse(data, function(err, tree) {
+        }, function(err, output) {
             if (err) {
+                console.error(String(err));
                 next(err);
                 return;
             }
 
             res.setHeader("Content-Type", "text/css");
-            res.send(tree.toCSS());
+            res.send(output.css);
         });
     });
 });