Tests: Replace space with dash in header name

Node.js has forbidden header names with spaces in
6192c9892f.

The next error is thrown when the test sets the "some header" header:
Uncaught TypeError: Header name must be a valid HTTP Token ["some header"]

To fix it, replace spaces with dashes.

test/test-memory.js

@@ -59,7 +59,7 @@ describe('memory usage', function() {
         cors_api_url + 'http://127.0.0.1:' + server.address().port);
     request.agent = false; // Force Connection: Close
     request.headers = {
-      'Long header': new Array(requestSize * 1e3).join('x'),
+      'Long-header': new Array(requestSize * 1e3).join('x'),
     };
     (function requestAgain() {
       if (remaining-- === 0) {