[ travis ] fix typo in bash

Author: gallais

travis/install_agda.sh

@@ -8,7 +8,7 @@ if ! type "agda" > /dev/null || [ ! `agda -V | sed "s/[^2]*//"` = "$AGDA_VERSION
 fi
 
 mkdir -p $HOME/.agda
-cp libraries-${VERSION} $HOME/.agda/
+cp libraries-${AGDA_VERSION} $HOME/.agda/
 cd $HOME/.agda/
 wget https://github.com/agda/agda-stdlib/archive/v0.17.tar.gz
 tar -xvzf v0.17.tar.gz