R with hugo v0.54.0: `GLIBCXX_3.4.20` and `GLIBCXX_3.4.21' not found

Hi @jeroen and @jimhester

hugo v0.54.0 seems to need additional libraries:

Hugo has been installed to /home/travis/bin
[1] TRUE
hugo: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.20' not found (required by hugo)
hugo: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by hugo)
Error in if (grepl(r, x)) return(as.numeric_version(gsub(r, "\\1", x))) : 
  argument is of length zero

(Travis build#L1353)

Trying to install these manually is a huge mess for me as all of my attempts to fix this issue on my own failed (for a history of failures see my last Travis builds).

Thus my question: could you integrate the required libraries (as the R blogdown package will stop working on the current R Travis-CI) ?

Solved by @yihui https://github.com/yihui/travis-blogdown/issues/1