fix: correct variable declaration

plugins/app-json/internal-functions

@@ -7,7 +7,7 @@ source "$PLUGIN_AVAILABLE_PATH/ps/functions"
 
 get_phase_script() {
   declare desc="extracts app.json from app image and returns the appropriate json key/value"
-  declare IMAGE_TAG="$1" PHASE_SCRIPT_KEY="$2"
+  declare IMAGE="$1" PHASE_SCRIPT_KEY="$2"
   local APP_JSON_FILE=$(mktemp "/tmp/dokku-${DOKKU_PID}-${FUNCNAME[0]}.XXXXXX")
   trap "rm -rf '$APP_JSON_FILE' >/dev/null" RETURN INT TERM