asymptote: disable install parallelism

Without the change parallel installs fail as:

...-coreutils-9.1/bin/install: cannot stat 'asy-keywords.el': No such file or directory
make: *** [Makefile:272: install-asy] Error 1

pkgs/tools/graphics/asymptote/default.nix

···
   '';
 
   enableParallelBuilding = true;
+  # Missing install depends:
+  #   ...-coreutils-9.1/bin/install: cannot stat 'asy-keywords.el': No such file or directory
+  #   make: *** [Makefile:272: install-asy] Error 1
+  enableParallelInstalling = false;
 
   meta = with lib; {
     description =  "A tool for programming graphics intended to replace Metapost";