rename spdy-csr.pem to spdy-ca.pem in example code

imho the 'ca' cert is a proof that your certificate issuer is a recognized intermediate certificate authority, and '-csr' in the filename would incorrectly hint at a Certificate Signing Request, which is something you send to your CA, not something you would use during operation.
Merge pull request #94 from michielbdejong/patch-1

rename spdy-csr.pem to spdy-ca.pem in example code