[skip appveyor] Pin libgap to 4.8.3

Author: isuruf

bin/install_travis.sh

@@ -12,5 +12,5 @@ if [[ "${WITH_SAGE}" == "yes" ]]; then
 fi
 
 conda update -q -n root conda
-conda install ${conda_pkgs}
+conda install ${conda_pkgs} libgap=4.8.3
 source activate $our_install_dir;