Cleanup XML warnings

[rgwilton]

The XML warnings (and YANG warnings) are now clean. I've not checked ID-Nits.

[rgwilton]

RW: I think that we need to check/fix some of these as part of last call (e.g., the doc shepherd should check them). but I don't think that we need to necessarily fix them before last call. Fixing the reference to YANG instance-data is trivial and should be done (now is).

Updated idnits:

idnits 2.17.1

draft-ietf-netmod-yang-module-versioning.txt:

Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info):

 No issues found here.

Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt:

== Mismatching filename: the document gives the document name as 'draft-ietf-netmod-yang-module-versioning-08', but the file name used is 'draft-ietf-netmod-yang-module-versioning'

Checking nits according to https://www.ietf.org/id-info/checklist :

 No issues found here.

Miscellaneous warnings:

 (Using the creation date from RFC6020, updated by this document, for
 RFC5378 checks: 2008-05-14)

-- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.)

Checking references for intended status: Proposed Standard

 (See RFCs 3967 and 4897 for information about using normative references
 to lower-maturity documents in RFCs)

== Missing Reference: 'RFCXXXX' is mentioned on line 1508, but not defined

 Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--).

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