define activate_env before rest of build script

Author: JacksonBurns

.conda/build.sh

@@ -1,5 +1,7 @@
 set -x
 
+ACTIVATE_ENV="${PREFIX}/etc/conda/activate.d/env_vars.sh"
+
 if [ -f "$ACTIVATE_ENV" ]; then
         echo 'python-jl -c "import julia; julia.install()"' >> $ACTIVATE_ENV
         # echo 'sed -i \'/julia.install/d\' $ACTIVATE_ENV' >> $ACTIVATE_ENV