Check dead links?

[onmax]

for example: /^https?://nimiq-slackin.herokuapp.com/,

/^https://medium.com/u/d3191ca07046?source=post_page-----b6b90c0bb1d5----------------------$/,
/^https://medium.com/u/57600910a883?source=post_page-----b6b90c0bb1d5----------------------$/,

#174 (comment)
#174 (comment)