Fix some issues reported by lintian

Fix some issues reported by lintian

• debian/copyright: use spaces rather than tabs to start continuation lines. (tab-in-license-text)
• Update watch file format version to 4. (older-debian-watch-file-standard)
• Set upstream metadata fields: Repository-Browse. (upstream-metadata-file-is-missing)
• Update standards version to 4.6.2, no changes needed. (out-of-date-standards-version)

Debdiff

These changes affect the binary packages:

[The following lists of changes regard files as different if they have different names, permissions or owners.]

Files in first set of .debs but not in second

lrwxrwxrwx  root/root   /usr/share/doc/python-jsonschema-doc/html/_static/sphinx_highlight.js -> ../../../../javascript/sphinxdoc/1.0/sphinx_highlight.js

Control files of package python-jsonschema-doc: lines which differ (wdiff format)

• Depends: libjs-sphinxdoc (>= 5.2) 5.0)

No differences were encountered between the control files of package **python3-jsonschema**

You can also view the diffoscope diff (unfiltered).

This merge proposal was created by the Janitor bot, and it will automatically rebase or close this proposal as appropriate when the target branch changes. Any comments you leave here will be read by the Janitor's maintainers.

Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/python-jsonschema/81136490-f7da-48e5-a22f-e638763e2f8b.