r-httpuv: add missing zlib.dev dependency to fix the build

pkgs/development/r-modules/default.nix

···
     runjags = [ pkgs.jags ];
     RVowpalWabbit = with pkgs; [ zlib.dev boost ];
     rzmq = with pkgs; [ zeromq pkg-config ];
+    httpuv = [ pkgs.zlib.dev ];
     clustermq = [ pkgs.zeromq ];
     SAVE = with pkgs; [ zlib bzip2 icu xz pcre ];
     sdcTable = with pkgs; [ gmp glpk ];