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/setup.js

@@ -49,7 +49,7 @@ nock('http://example.com')
 
   .get('/redirecttarget')
   .reply(200, 'redirect target', {
-    'Some header': 'value'
+    'Some-header': 'value'
   })
 
   .head('/redirect')