crypto/x509: Correction of incrorrect default version number in TBSCertificateList and Certificate.CreateCRL

RFC5280 states:

"This optional field describes the version of the encoded CRL.  When
 extensions are used, as required by this profile, this field MUST be
 present and MUST specify version 2 (the integer value is 1)."

This CL has been discussed at: http://golang.org/cl/172560043

Change-Id: I8a72d7593d5ca6714abe9abd6a37437c3b69ab0f
Reviewed-on: https://go-review.googlesource.com/2259Reviewed-by: Adam Langley <agl@golang.org>