[docs] fix broken links in pkgdown

[jameslamb]

Inspired by microsoft/LightGBM#3036.

I never noticed it, but the Source: links on our pkgdown site are broken right now. For example, go to https://uptake.github.io/uptasticsearch/reference/es_search.html and click the link R/es_search.Rafter Source:.

pkgdown creates these links automatically if you have a GitHub link in URL or BugReports in DESCRIPTION. It then assumes that the R package is at the repo root (like most only-an-R-package repos). So this has probably been broken since we added Python...only a couple years 😬

The changes in this PR were produced by upgrading to pkgdown 1.5.1 and running make gh_pages from the root of the repo. Most of the changes are miscellaneous "pkgdown was updated" things, but the main change to fix the links is in _pkgdown.yml:

repo:
  url:
    home: https://github.com/uptake/uptasticsearch/
    source: https://github.com/uptake/uptasticsearch/tree/master/r-pkg/
    issue: https://github.com/uptake/uptasticsearch/issues
    user: https://github.com/

[codecov-io]

Codecov Report

Merging #212 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #212   +/-   ##
=======================================
  Coverage   93.13%   93.13%           
=======================================
  Files           8        8           
  Lines         597      597           
=======================================
  Hits          556      556           
  Misses         41       41           

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[austin3dickey]

nice, whoops!