Invalid URLs in vignette

Hi,
While checking the package I get :
```
Found the following (possibly) invalid URLs:
URL: http://r.iresmi.net/2019/05/11/kernel-spatial-smoothing-transforming-points-pattern-to-continuous-coverage/ (moved to https://r.iresmi.net/posts/2019/kernel_spatial_smoothing_transforming_points_pattern_to_continuous_coverage/)
From: inst/doc/btb.html
Status: 200
Message: OK
URL: https://githubmemory.com/repo/SNStatComp/awesome-official-statistics-software
From: inst/doc/btb.html
Status: Error
Message: libcurl error code 7:
Failed to connect to githubmemory.com port 443 after 111 ms: Couldn't connect to server
URL: https://inspire.ec.europa.eu/ (moved to https://knowledge-base.inspire.ec.europa.eu/index_en)
From: inst/doc/btb.html
Status: 200
Message: OK
URL: https://mobile.twitter.com/DavidZumbach/status/1373166163497213952
From: inst/doc/btb.html
Status: 403
Message: Forbidden
URL: https://mobile.twitter.com/raffverduzco/status/1128075094524350464?lang=bg
From: inst/doc/btb.html
Status: 403
Message: Forbidden
```
(for the last 2, Twitter is no longer accessible without an user account)