self-upgrade revert back

lib/self-upgrade.bash

@@ -9,10 +9,15 @@
 
 function self_upgrade {
   mv "$MIAOU_BASH_DIR" "$MIAOU_BASH_DIR".before_upgrade
-  "$MIAOU_BASH_DIR".before_upgrade/install.sh upgraded
-  rm -rf "$MIAOU_BASH_DIR".before_upgrade
-  echo -n "version: "
-  . "$MIAOU_BASH_DIR"/bin/miaou-bash --version
+  if "$MIAOU_BASH_DIR".before_upgrade/install.sh upgraded; then
+    rm -rf "$MIAOU_BASH_DIR".before_upgrade
+    echo -n "version: "
+    . "$MIAOU_BASH_DIR"/bin/miaou-bash --version
+  else
+    echo "ERROR: trouble during self-upgrade: revert back"
+    rm -rf "$MIAOU_BASH_DIR"
+    mv "$MIAOU_BASH_DIR".before_upgrade "$MIAOU_BASH_DIR"
+  fi
 }
 
 # MAIN