migrate mosaic home to xdg config path

bin/mosaic-upgrade-slaves

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-MOSAIC_HOME="${MOSAIC_HOME:-$HOME/.mosaic}"
+MOSAIC_HOME="${MOSAIC_HOME:-$HOME/.config/mosaic}"
 BOOTSTRAP_CMD="$MOSAIC_HOME/bin/mosaic-bootstrap-repo"
 
 roots=("$HOME/src")
@@ -45,7 +45,7 @@ done
 
 if [[ ! -x "$BOOTSTRAP_CMD" ]]; then
   echo "[mosaic-upgrade] Missing bootstrap command: $BOOTSTRAP_CMD" >&2
-  echo "[mosaic-upgrade] Install/refresh framework first: ~/.mosaic/install.sh" >&2
+  echo "[mosaic-upgrade] Install/refresh framework first: ~/.config/mosaic/install.sh" >&2
   exit 1
 fi