BLD: fix conda version to 4.3.30 (#18838)

Author: jreback

ci/install_travis.sh

@@ -48,7 +48,9 @@ echo
 echo "[update conda]"
 conda config --set ssl_verify false || exit 1
 conda config --set quiet true --set always_yes true --set changeps1 false || exit 1
-conda update -q conda
+
+conda install conda=4.3.30
+# conda update -q conda
 
 if [ "$CONDA_BUILD_TEST" ]; then
     echo